Pulsed laser diode driver

ABSTRACT

A pulsed laser diode driver includes an inductor having a first terminal configured to receive a source voltage. A source capacitor has a first terminal connected to the first terminal of the inductor to provide the source voltage. A bypass switch has a drain node connected to a second terminal of the inductor and to a first terminal of a bypass capacitor. A laser diode has an anode connected to the second terminal of the inductor and to the drain node of the bypass switch. A laser diode switch has a drain node connected to a cathode of the laser diode. The laser diode switch and the bypass switch control a current flow through the inductor to produce a high-current pulse through the laser diode, the high-current pulse corresponding to a peak current of a resonant waveform developed at the anode of the laser diode.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/994,470, filed Mar. 25, 2020 and to U.S. Provisional Application No.63/127,794, filed Dec. 18, 2020, all of which are incorporated byreference for all purposes.

BACKGROUND

Laser-based ranging systems, such as Lidar, often use a pulsed laserdiode driver circuit to generate a short, high-current pulse, which ispassed through a laser diode to emit a corresponding pulse of laserlight. Reflected pulses of laser light are received by the Lidar systemand used to determine a distance between the Lidar system and the pointof reflection. Spatial resolution of Lidar systems is determined in partby the width of the pulse of laser light. Thus, it is usually desirableto generate a pulse of light having a width of about 5 ns or less.However, parasitic inductances of the pulsed laser diode driver circuitand the laser diode typically must be overcome to achieve the desiredshort pulse width. For example, many laser diodes have at least one bondwire which can contribute 1 nH of inductance, thereby limiting a slewrate of the current pulse unless there is very high voltage. Thus, someconventional pulsed laser diode driver circuits use a high sourcevoltage, often greater than 40V-100V, to achieve the desired pulsewidth. Switching devices, such as GaN field-effect transistors (FET) areoften used in conventional pulsed laser diode driver circuits as theycan withstand such high voltages. However, pulsed laser diode drivercircuits that use GaN technology may be more expensive, and/or may bemore difficult to integrate with Silicon-based architectures.

SUMMARY

In some embodiments, a pulsed laser diode driver includes a firstinductor having a first terminal and a second terminal. The firstterminal of the first inductor is configured to receive a first sourcevoltage, the first source voltage being based on a DC input voltage. Afirst source capacitor has a first terminal directly electricallyconnected to the first terminal of the first inductor to provide thefirst source voltage, and a second terminal electrically coupled toground. A first bypass switch has a drain node that is directlyelectrically connected to the second terminal of the first inductor anda source node that is directly electrically connected to ground. A firstbypass capacitor has a first terminal directly electrically connected tothe drain node of the first bypass switch. A first laser diode has ananode and a cathode. The anode of the first laser diode is directlyelectrically connected to the second terminal of the first inductor andto the drain node of the first bypass switch. A first laser diode switchhas a drain node that is directly electrically connected to the cathodeof the first laser diode and a source node that is directly electricallyconnected to ground. The first laser diode switch and the first bypassswitch are configured to control a current flow through the firstinductor to produce a high-current pulse through the first laser diode,the high-current pulse corresponding to a peak current of a resonantwaveform developed at the anode of the first laser diode.

In some embodiments, a pulsed laser diode driver includes an inductorhaving a first terminal and a second terminal. The first terminal of theinductor is configured to receive a source voltage. A source capacitorhas a first capacitor terminal that is directly electrically connectedto the first terminal of the inductor to provide the source voltage anda second capacitor terminal electrically coupled to a bias voltage node.A source switch has a first terminal that is directly electricallyconnected to a DC input voltage terminal and a second terminal that isdirectly electrically connected to the first capacitor terminal. Thesource switch is operable to charge the source capacitor when the sourceswitch is enabled. A bypass switch has a drain node that is directlyelectrically connected to the second terminal of the inductor and asource node that is directly electrically connected to the bias voltagenode. A laser diode switch has a drain node that is directlyelectrically connected to the second terminal of the inductor and to thedrain node of the bypass switch. A laser diode has an anode that isdirectly electrically connected to a source node of the laser diodeswitch and a cathode that is directly electrically connected to the biasvoltage node. A bypass capacitor has i) a first terminal directlyelectrically connected to the second terminal of the inductor and asecond terminal directly electrically connected to the bias voltagenode, ii) a first terminal directly electrically connected to the anodeof the laser diode and a second terminal directly electrically connectedto the bias voltage node, iii) a first terminal directly electricallyconnected to the second terminal of the inductor and a second terminaldirectly electrically connected to the second capacitor terminal of thesource capacitor, or iv) a first terminal directly electricallyconnected to the anode of the laser diode and a second terminal directlyelectrically connected to the second capacitor terminal of the sourcecapacitor. The laser diode switch and the bypass switch are configuredto control a current flow through the inductor to produce a high-currentpulse through the laser diode, the high-current pulse corresponding to apeak current of a resonant waveform developed at the anode of the laserdiode.

In some embodiments, a pulsed laser driver includes an inductor having afirst terminal and a second terminal, the first terminal beingconfigured to receive a source voltage. A source capacitor has a firstcapacitor terminal directly electrically connected to the first terminalof the inductor to provide the source voltage and a second capacitorterminal electrically coupled to a bias voltage node. A source switchhas a first terminal that is directly electrically connected to a DCinput voltage terminal and a second terminal that is directlyelectrically connected to the first capacitor terminal. The sourceswitch is operable to charge the source capacitor when the source switchis enabled. A bypass switch has a drain node that is directlyelectrically connected to the second terminal of the inductor and asource node that is directly electrically connected to the bias voltagenode. A laser diode has an anode and a cathode, the anode being directlyelectrically connected to the second terminal of the inductor and to thedrain node of the bypass switch. A laser diode switch has a drain nodethat is directly electrically connected to the cathode of the laserdiode and a source node that is directly electrically connected to thebias voltage node. A bypass capacitor has i) a first terminal directlyelectrically connected to the second terminal of the inductor and asecond terminal directly electrically connected to the bias voltagenode, ii) a first terminal directly electrically connected to the secondterminal of the inductor and a second terminal directly electricallyconnected to the second capacitor terminal of the source capacitor, oriii) a first terminal directly electrically connected to the anode ofthe laser diode and a second terminal directly electrically connected tothe cathode of the laser diode. The laser diode switch and the bypassswitch are configured to control a current flow through the inductor toproduce a high-current pulse through the laser diode, the high-currentpulse corresponding to a peak current of a resonant waveform developedat the anode of the laser diode.

In some embodiments, a pulsed laser diode driver includes multipleinductors, each inductor having a first terminal and a second terminal,the first terminal of each inductor being configured to receive arespective source voltage. The pulsed laser diode driver includesmultiple source capacitors, each source capacitor corresponding to arespective inductor and having a first capacitor terminal directlyelectrically connected to the first terminal of that respective inductorto provide the source voltage and a second capacitor terminalelectrically coupled to a bias voltage node. The pulsed laser diodedriver includes multiple bypass switches, each bypass switchcorresponding to a respective inductor and having a drain node that isdirectly electrically connected to the second terminal of thatrespective inductor and a source node that is directly electricallyconnected to the bias voltage node. The pulsed laser diode driverincludes multiple laser diodes, each laser diode corresponding to arespective inductor and a respective bypass switch and having an anodeand a cathode, the anode being directly electrically connected to thesecond terminal of that respective inductor and to the drain node ofthat respective bypass switch. A laser diode switch has a drain nodethat is directly electrically connected to the cathode of each of thelaser diodes and a source node that is directly electrically connectedto the bias voltage node. The pulsed laser diode driver includesmultiple bypass capacitors, each bypass capacitor corresponding to arespective inductor and having a first terminal directly electricallyconnected to the second terminal of that respective inductor and asecond terminal directly electrically connected to the bias voltagenode. The laser diode switch and the multiple bypass switches areconfigured to control a respective current flow through each of theinductors to produce a respective high-current pulse through each of thelaser diodes, each of the high-current pulses corresponding to a peakcurrent of a resonant waveform developed at the anode of a respectivelaser diode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are simplified circuit schematics of pulsed laser diodedrivers of a first general topology, in accordance with someembodiments.

FIGS. 2A-2D show simplified plots of signals related to operation of thepulsed laser diode driver shown in FIG. 1A, in accordance with someembodiments.

FIG. 3 is a portion of an example switching sequence for operation ofthe pulsed laser diode drivers shown in FIGS. 1A-1C, in accordance withsome embodiments.

FIGS. 4A-4D are simplified circuit schematics of pulsed laser diodedrivers of a second general topology, in accordance with someembodiments.

FIGS. 5A-5D are simplified circuit schematics of pulsed laser diodedrivers of a third general topology, in accordance with someembodiments.

FIGS. 6A-6D are simplified circuit schematics of pulsed laser diodedrivers of a fourth general topology, in accordance with someembodiments.

FIGS. 7A-7E are simplified circuit schematics of pulsed laser diodedrivers of a fifth general topology, in accordance with someembodiments.

FIGS. 8A-8B are simplified circuit schematics of pulsed laser diodedrivers of a sixth general topology, in accordance with someembodiments.

FIGS. 9A-9B are simplified circuit schematics of pulsed laser diodedrivers of a seventh general topology, in accordance with someembodiments.

FIGS. 10A-10B are simplified circuit schematics of pulsed laser diodedrivers of an eighth general topology, in accordance with someembodiments.

FIGS. 11-12 show simplified plots of signals related to operation of thepulsed laser diode driver shown in FIG. 10B, in accordance with someembodiments.

FIGS. 13A-13I are simplified circuit schematics of high-repetition-ratepulsed laser diode drivers, in accordance with some embodiments.

FIG. 14 shows simplified plots of signals related to operation of thepulsed laser diode driver shown in FIG. 13I, in accordance with someembodiments.

FIG. 15 shows a simplified circuit schematic of a pulsed laser diodedriver of a ninth general topology, in accordance with some embodiments.

FIGS. 16A-16B show simplified plots of signals related to operation ofthe pulsed laser diode driver shown in FIG. 15, in accordance with someembodiments.

FIGS. 17, 18, 19, and 20 are simplified circuit schematics of pulsedlaser diode drivers having an adjustable DC input voltage, in accordancewith some embodiments.

FIGS. 21A-21B are simplified plots of signals related to operation ofthe pulsed laser diode drivers shown in FIGS. 17, 18, 19, and 20.

DETAILED DESCRIPTION

In accordance with some embodiments, pulsed laser diode driver circuitsdisclosed herein (“pulsed laser diode drivers”), generate high-current(e.g., 40 Amp) ultra-short pulses (e.g., 1-5 ns) to emit a laser pulsefrom a laser diode using a tunable resonant circuit, as compared toconventional solutions that rely on fixed, and often unavoidable,parasitic capacitances and inductances of a circuit. The tunableresonant circuit provides easily tunable parameters which control apulse width, a peak current, a charge time, a recovery time, a decaytime, and other tunable parameters of the pulsed laser diode driver.Embodiments of a switching sequence to drive the pulsed laser diodedrivers disclosed herein are operable to generate a resonant waveform atan anode of the laser diode to produce the high-current pulse throughthe laser diode, a voltage level of the resonant waveform beingadvantageously sufficient to support the high-current pulse and not of avoltage level that exceeds the voltage required to generate thehigh-current pulse.

Thus, embodiments of such pulsed laser diode drivers can advantageouslygenerate the high-current pulses using a low input voltage (e.g., 6V,9V, 15V, etc.) and can thereby use Silicon-based switches, rather thanGaN-based switches which are used by many conventional solutions. Any ofthe pulsed laser diode drivers disclosed herein can therefore beintegrated into a single semiconductor die. Embodiments of pulsed laserdiode drivers disclosed herein advantageously use a discrete inductor(e.g., a through-hole or surface-mounted component) intentionally addedto the pulsed laser diode driver to generate a resonant waveform ratherthan relying on parasitic inductances (e.g., of the laser diode, of bondwires, or inter-circuit connections) of the pulsed laser diode driver.As a result, embodiments of the laser drivers disclosed herein areeasily tunable and have a reproducible architecture. By contrast,conventional pulsed laser diode drivers often use a variety oftechniques to overcome the effects of parasitic inductances of thepulsed laser diode driver and of the laser diode itself and thereforeteach away from intentionally adding yet additional inductance to thepulsed laser diode driver. In addition to such intentionally addedinductors, the pulsed laser diode drivers disclosed hereinadvantageously include a bypass capacitor that may be used by a designerto easily tune a desired pulse width emitted by the laser diode, ascompared to conventional solutions which only have a source capacitor,or that only consider non-tunable parasitic capacitances of the pulsedlaser diode driver. Once again, such conventional solutions teach awayfrom adding yet additional capacitance to the pulsed laser diode driver.Because conventional solutions rely on parasitic capacitances andinductances of the conventional laser driver, modifying parameters suchas a pulse width might require a redesign or re-layout of theconventional solution. By comparison, parameters, such as a pulse width,of the pulsed laser diode drivers disclosed herein can be tuned bysimply changing a component value.

Multi-channel laser diodes are conventionally produced on a singlemonolithic substrate housed in a laser diode package. Conventionally, asingle pin of the laser diode package is connected to all of the laserdiode cathodes as a group (i.e., “common cathode”), whereas each laserdiode anode is individually connected to a respective pin of the laserdiode package. Pulsing each laser diode independently conventionallyrequires a switch in the laser diode anode current path to select whichlaser diode fires. However, an N-type switch conventionally requires abootstrap circuit to level-shift a gate drive of that switch when thelaser diode current path is enabled. Such bootstrap circuitry addscomplexity and cost to a pulsed laser diode driver design. Thus,disclosed herein are embodiments of a multi-channel pulsed laser diodedriver circuit for independently driving laser diodes of a commoncathode multi-channel laser diode package advantageously using N-typeswitches without any bootstrap circuitry.

A repetition rate of a multi-channel laser diode driver, as well as ofeach of the pulsed laser diode drivers described herein, is limited by acharging time of each channel's source capacitor which is describedbelow. The pulsed laser diode drivers described herein create narrow(e.g., 1-5 nsec) high-current pulses (e.g., 40 amp) through a drivenlaser diode. The instantaneous power in the driven laser diode istherefore high (e.g., in the order of hundreds of watts). For manyapplications (e.g., Lidar), the duty cycle of the pulse is generally0.01% or less to limit a total power dissipated in the laser diode,which results in an upper limit to a repetition rate. In conventionalpulsed laser diode driver applications, a resistor is used to chargesource capacitors during each cycle. In such conventional solutions, anRC time constant of charging circuits is typically not an issue becausethe duty cycle is so low. However, for applications that require ahigher repetition rate for laser pulses, the RC time constant ofconventional charging circuits creates an undesirable limitation. Thus,in any of the embodiments disclosed herein, each source resistor of agiven laser diode driver may be advantageously replaced by an activelycontrolled source switch that quickly charges an associated sourcecapacitor.

Typical resonant driver designs require a damping resistor to minimizeringing duration. However, the added damping resistor dissipates powerwhich lowers the overall power efficiency of the design. Thus, in someembodiments, a pulsed laser diode driver is disclosed thatadvantageously switches a damping resistor into the resonant circuitduring portions of a switching sequence during which the dampingresistor critically damps ringing, and switches the damping resistor outof the resonant circuit during portions of the switching sequence whenthe damping resistor is not providing a positive benefit to the resonantcircuit, thereby increasing an overall power efficiency of the pulsedlaser diode driver as compared to one that includes a damping resistorfor the entirety of a switching sequence.

For some applications, the amplitude of a high-current pulse deliveredby a pulsed laser diode driver, such as any of those disclosed herein,may need to be adjusted in amplitude from pulse to pulse. Thus, in someembodiments, any of the pulsed laser diode drivers disclosed herein maybe advantageously configured to adjust an amplitude of the high-currentpulse delivered to one or more laser diodes on a pulse-to-pulse basis.

FIGS. 1A-C are simplified circuit schematics of pulsed laser diodedrivers 101-103 of a first general topology to drive a laser diode usinga low-side switch, in accordance with some embodiments. The pulsed laserdiode drivers 101-103 each generally include a source resistor R_(S), asource capacitor C_(S) (i.e., a physical component that is notrepresentative of a parasitic capacitance of another component), adamping resistor R_(Damp), an inductor L_(S) (i.e., a physical componentthat is not representative of a parasitic inductance of anothercomponent), a bypass capacitor C_(BP) (i.e., a physical component thatis not representative of a parasitic capacitance of another component),a laser diode D_(L), a bypass switch M_(BP), and a laser diode switchM_(DL). The laser diode switch M_(DL) is configured as a low-sideswitch. Also shown is a controller 120, nodes 110, 112, a parasiticinductance L_(DL) of the laser diode D_(L), a DC input voltage V_(in), asource voltage V_(S) at the source capacitor C_(S), a current i_(LS)through the inductor L_(S), a current i_(DL) through the laser diodeD_(L), a bypass switch gate driver signal GATE_(BP), and a laser diodeswitch gate driver signal GATE_(DL).

Topologies of the pulsed laser diode drivers 101-103 vary with respectto the placement of the bypass capacitor C_(BP). In each of thetopologies of the pulsed laser diode drivers 101-103, a first terminalof the source resistor R_(S) is configured to be directly electricallyconnected to the DC input voltage V_(in). A first terminal of the sourcecapacitor C_(S) is directly electrically connected to a second terminalof the source resistor R_(S), and a second terminal of the sourcecapacitor C_(S) is directly electrically connected to a first terminalof the damping resistor R_(Damp). A second terminal of the dampingresistor R_(Damp) is directly electrically connected to a bias voltagenode such as ground. Thus, the second terminal of the source capacitorC_(S) is electrically coupled to the bias voltage node. A first terminalof the inductor L_(S) is directly electrically connected to the secondterminal of the source resistor R_(S) and to the first terminal of thesource capacitor C_(S). A drain node of the bypass switch M_(BP) isdirectly electrically connected to a second terminal of the inductorL_(S), and a source node of the bypass switch M_(BP) is directlyelectrically connected to the bias voltage node. An anode of the laserdiode D_(L) is directly electrically connected to the second terminal ofthe inductor L_(S), and a cathode of the laser diode D_(L) is directlyelectrically connected to a drain node of the laser diode switch M_(DL).A source node of the laser diode switch M_(DL) is directly electricallyconnected to the bias voltage node.

The bypass switch M_(BP) is configured to receive the bypass switch gatedriver signal GATE_(BP) at a gate node, the bypass switch gate driversignal GATE_(BP) being operable to turn the bypass switch M_(BP) on oroff based on a voltage level of the bypass switch gate driver signalGATE_(BP). Similarly, the laser diode switch M_(DL) is configured toreceive the laser diode switch gate driver signal GATE_(DL) at a gatenode, the laser diode switch gate driver signal GATE_(DL) being operableto turn the laser diode switch M_(DL) on or off based on a voltage levelof the laser diode switch gate driver signal GATE_(DL). In someembodiments, the pulsed laser diode driver circuits disclosed hereininclude one or more bootstrap circuits or other level-shifting circuitsto drive one or more high-side switches. Either or both of the bypassswitch M_(BP) and the laser diode switch M_(DL) can be implemented asN-type switches or P-type switches. In some embodiments, the bypassswitch M_(BP) and the laser diode switch M_(DL) are implemented asSilicon-based or Silicon-Carbide-based field-effect transistors (FETs).Two or more components described herein as having terminals that aredirectly electrically connected have a DC current path between therespective terminals of the two or more components. For example, a firstand second component are not directly electrically connected via acapacitor or inductor connected in series between the first componentand the second component.

As shown in the simplified circuit schematic of the pulsed laser diodedriver 101 of FIG. 1A, in some embodiments a first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to the anode of the laser diodeD_(L). In such embodiments, a second terminal of the bypass capacitorC_(BP) is directly electrically connected to the bias voltage node. Asshown in the simplified circuit schematic of the pulsed laser diodedriver 102 of FIG. 1B, in some embodiments, the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to the anode of the laser diodeD_(L). The second terminal of the bypass capacitor C_(BP) is directlyelectrically connected to the second terminal of the source capacitorC_(S) and to the first terminal of the damping resistor R_(Damp). Asshown in the simplified circuit schematic of the pulsed laser diodedriver 103 of FIG. 1C, in some embodiments, the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to the anode of the laser diodeD_(L). In such embodiments, the second terminal of the bypass capacitorC_(BP) is directly electrically connected to the drain terminal of thelaser diode switch M_(DL) and to the cathode of the laser diode D_(L).

In some embodiments, the pulsed laser diode drivers 101-103 areconfigured to receive the DC input voltage V_(in) having a voltage rangefrom about 10V to 20V, which is advantageously lower than an inputvoltage used by many conventional pulsed laser diode drivers. Theinductor L_(S) is a physical component added to the pulsed laser diodedrivers 101-103 (i.e., as opposed to a representation of a parasiticinductance caused by components or interconnections such as bond wires).Similarly, the bypass capacitor C_(BP) is a physical component added tothe pulsed laser diode drivers 101-103 (i.e., as opposed to arepresentation of a parasitic capacitance). One advantage of usingphysical inductor and capacitor components rather than using parasiticinductances is that values of the inductor L_(S) and the bypasscapacitor C_(BP) can be easily modified by a designer or even anend-user. By comparison, conventional designs that rely on parasiticreactances may require re-design and/or re-layout to change an operatingparameter.

As disclosed herein, values of the DC input voltage V_(in), theinductance of the inductor L_(S), the capacitance of the sourcecapacitor C_(S), the resistance of the damping resistor R_(Damp), andthe capacitance of the bypass capacitor C_(BP) can advantageously beselected (“tuned”) to achieve a desired operation of the pulsed laserdiode drivers 101-103 (e.g., a charge time, a pulse width, a pulsevoltage, a pulse current). For example, a pulse width of the currenti_(DL) flowing through the laser diode D_(L) can be tuned by adjustingthe capacitance value of the bypass capacitor C_(BP). A peak currentlevel of the pulse of current i_(DL) flowing through the laser diodeD_(L) can be tuned by adjusting the source voltage V_(S) on the supplycapacitor C_(S). A capacitance value of the source capacitor C_(S) canbe tuned to adjust a timing delay of the current pulse and an upperrange of the current i_(DL) through the laser diode D_(L). Resistancevalues of the damping resistor R_(Damp) are dependent on the capacitancevalue of the supply capacitor C_(S) and can be tuned within a range ofvalues such that at a lower resistance, a lower frequency resonance ofthe pulsed laser diode drivers disclosed herein is underdamped (e.g., atabout R_(Damp)=0.1 Ohm), or is critically damped (e.g., at aboutR_(Damp)=0.4 Ohm). The damping resistor R_(Damp) is operable to preventcurrent of the generated resonant waveform from becoming negative whichcould thereby enable a body diode of the bypass switch M_(BP) or thelaser diode switch M_(DL). Although a resulting maximum current level ofthe current i_(DL) through the laser diode D_(L) is lower for thecritically damped case, the current level can be easily adjusted byraising the voltage level of the DC input voltage V_(in). In otherembodiments, the damping resistor R_(Damp) is removed entirely from thedesign (i.e., the second terminal of the source capacitor C_(S) isdirectly electrically connected to the bias voltage node). In yet otherembodiments, the resistance value of the damping resistor R_(Damp) isset to zero Ohms.

In some embodiments, the DC input voltage V_(in) is about 15V, theinductance of the inductor L_(S) is about 6 nH, the capacitance of thesource capacitor C_(S) is about 100 nF, the resistance of the dampingresistor R_(Damp) is about 0.1 Ohms, and the capacitance of the bypasscapacitor C_(BP) is about 1 nF. In some embodiments, a voltage at thefirst terminal of the damping resistor R_(Damp) is received by thecontroller 120 to provide an indication of a current flow through thedamping resistor R_(Damp).

In some or all of the embodiments disclosed herein, to produce around a40 A high-current pulse through the laser diode (or laser diodes) D_(L),the DC input voltage V_(in) may range from 10-15 volts. In some suchembodiments, the inductance of inductor L_(S) may range from 5-10 nH,the value of which determines the amount of flux delay to produce therequired current. In some such embodiments, the inductance of theinductor L_(S) is selected to be an order of magnitude greater than aparasitic inductance of a printed circuit board (PCB) in which thepulsed laser diode driver is implemented. In some embodiments, theresistance of the damping resistor R_(S) ranges from 100-200 mOhm. Acapacitance of the bypass capacitor C_(BP) determines the pulse width ofthe high-current pulse through the laser diode(s) D_(L), and in someembodiments ranges in capacitance from 1-5 nF. In some such embodiments,a capacitance of the supply capacitor C_(S) ranges from 25-100 nFdepending on a peak current of the high-current pulse through the laserdiode(s) D_(L) that is required or desired. The smaller the supplycapacitor C_(S), the higher the DC input voltage V_(in) is needed to getthe required or desired peak current of the high-current pulse throughthe laser diode(s) D_(L). In some such embodiments, a smallestcapacitance value of the supply capacitor C_(S) that can still deliverthe needed or desired peak current of the high-current pulse through thelaser diode(s) D_(L) is selected because all the remaining energy afterthe high-current pulse is shunted to ground and is wasted, therebylowering a power efficiency of the pulsed laser diode driver.

The controller 120 may be integrated with any embodiment of the pulsedlaser diode drivers disclosed herein, or it may be a circuit or modulethat is external to any embodiment of the pulsed laser diode driversdisclosed herein. The controller 120 is operable to generate one or moregate drive signals having a voltage level that is sufficient to controlone or more laser diode switches M_(DL) and one or more bypass switchesM_(BP). Additionally, the controller 120 is operable to sense a voltageand/or current at any of the nodes 110 and 112 and at nodes that aresimilar to, or the same as, the nodes 110 and 112 as described herein,or at still other nodes of the pulsed laser diode drivers disclosedherein. The controller 120 may include one or more timing circuits,look-up tables, processors, memory, or other modules to control thepulsed laser diode drivers disclosed herein. Operation of the pulsedlaser diode drivers 101-103 is explained in detail with respect tosimplified plots 201-207 of FIGS. 2A-D and an example switching sequence300 shown in FIG. 3.

FIGS. 2A-2D show simplified plots 201-207 of signals related tooperation of the pulsed laser diode driver 101 shown in FIG. 1A, inaccordance with some embodiments. However, signals related to theoperation of the pulsed laser diode drivers 101-103, 401-404, 501-504,601-604, 701-705, 801-802, and 901-902 are similar to, or are the sameas, those shown in the simplified plots 201-207.

The simplified plot 201 illustrates a voltage plot of the bypass switchgate driver signal GATE_(BP) 220, a voltage plot of the laser diodeswitch gate driver signal GATE_(DL) 221, a current plot of the currenti_(LS) through the inductor L_(S) 222, a current plot of the currenti_(DL) through the laser diode D_(L) 223, and a voltage plot of thesource voltage V_(S) 224 at the source capacitor C_(S), all over thesame duration of time. Details of these signals are described below. Thevoltage plots of the bypass switch gate driver signal GATE_(BP) 220 andthe laser diode switch gate driver signal GATE_(DL) 221 have beenlevel-shifted for readability, but are, in actuality, low voltageinputs. Additionally, the voltage plots of the bypass switch gate driversignal GATE_(BP) 220 and the laser diode switch gate driver signalGATE_(DL) 221 assume that the laser diode switch M_(DL) and the bypassswitch M_(BP) are NFET devices. However, if PFET devices are usedinstead, the polarity of the bypass switch gate driver signal GATE_(BP)220 and the laser diode switch gate driver signal GATE_(DL) 221 areinverted.

Upon receiving (e.g., from the controller 120) an asserted level of thebypass switch gate driver signal GATE_(BP) 220 at the gate node of thebypass switch M_(BP), the bypass switch M_(BP) is enabled (i.e.,transitioned to an ON-state). Similarly, upon receiving (e.g., from thecontroller 120) an asserted level of the laser diode switch gate driversignal GATE_(DL) 221 at the gate node of the laser diode switch M_(DL),the laser diode switch M_(DL) is enabled. As highlighted in the plot202, when the bypass switch M_(BP) is enabled, the rising current i_(LS)222 begins to flow through the inductor L_(S), thereby building magneticflux at the inductor L_(S). When the current i_(LS) 222 has reached adesired level (e.g., as determined by the controller 120 using sensedcurrent, voltage, a timer circuit, or as determined by designconstraints), a de-asserted level of the bypass switch gate driversignal GATE_(BP) 220 is received (e.g., from the controller 120) at thegate node of the bypass switch M_(BP), thereby disabling the bypassswitch M_(BP) (i.e., transitioned to an OFF-state). As highlighted inthe plot 203, when the bypass switch M_(BP) is disabled, the currenti_(LS) 222 which has built up through the inductor L_(S), having noother current path, is redirected through the laser diode D_(L), causinga short (e.g., 1 ns-5 ns), high-current (e.g., >30 A) pulse to flowthrough the laser diode D_(L), thereby causing the laser diode D_(L) toemit a pulse of laser light. Because energy in the form of flux has beenstored at the inductor L_(S), the high-current pulse i_(DL) that flowsthrough the laser diode D_(L) can be significantly greater than thecurrent i_(LS) that flows through the inductor L_(S). Values of thereactive components of the laser diode drivers disclosed herein can beadvantageously selected to generate a desired current amplitude of thehigh-current pulse i_(DL).

After emission from the laser diode D_(L), the bypass switch M_(BP) isreenabled by an asserted level of the bypass switch gate driver signalGATE_(BP) 220, and the laser diode switch M_(DL) is maintained in anenabled state by an asserted level of the laser diode switch gate driversignal GATE_(DL) 221. As highlighted in the plot 204, the bypass switchM_(BP) and the laser diode switch M_(DL) are both advantageouslymaintained in the enabled state as the source voltage V_(S) 224 storedat the source capacitor C_(S) is discharged. As highlighted in the plot205, while the bypass switch M_(BP) and the laser diode switch M_(DL)are maintained in the enabled state, the current i_(DL) 223 through thelaser diode D_(L) (and importantly, through the parasitic inductanceL_(DL) of the laser diode D_(L)) diminishes to zero. Thereafter, boththe bypass switch M_(BP) and the laser diode switch M_(DL) are disabledby de-asserted levels (e.g., from the controller 120) of the bypassswitch gate driver signal GATE_(BP) 220 and the laser diode switch gatedriver signal GATE_(DL) 221. Because the laser diode switch M_(DL) isnot disabled until a current through the parasitic inductance L_(DL) ofthe laser diode D_(L) has diminished to zero, a high voltage spikeadvantageously does not develop at the anode of the laser diode D_(L) asthere is no rapid change in current through the parasitic inductanceL_(DL). Because such high voltage spikes are advantageously mitigated,the laser diode switch M_(DL) does not need to be selected to withstandhigh voltages, thereby simplifying the design and reducing the cost ofthe pulsed laser diode drivers disclosed herein as compared toconventional solutions. Additionally, because such high voltage spikesare mitigated, the pulsed laser diode drivers disclosed herein do notrequire voltage snubbing circuits that are commonly used in conventionalsolutions, thereby further simplifying the design and reducing the costof the pulsed laser diode drivers disclosed herein as compared toconventional solutions.

The high-current pulse 223 is a first and largest peak of the resonantwaveform developed by reactive components of the pulsed laser diodedriver circuit. These reactive components include the source capacitorC_(S), the inductor L_(S), the parasitic inductance L_(DL) of the laserdiode D_(L), and the bypass capacitor C_(BP). In addition to theadvantages described above, the bypass switch M_(BP) also reducessubsequent resonant waveform “ringing” of the resonant waveform afterthe high-current pulse 223 is generated. As shown in the plot 206, if abypass switch gate driver signal GATE_(BP) 220′ is not asserted after ahigh-current pulse i_(DL) 223′ is generated, ringing occurs on thecurrent i_(LS) 222′ through the inductor L_(S), on the current i_(DL)223′ through the laser diode D_(L), and on the source voltage V_(S) 224′at the source capacitor C_(S). As shown, the high-current pulse 223through the laser diode D_(L) corresponds to a peak (e.g., maximum, orlocal maximum, amplitude) current of a resonant waveform of currenti_(DL) 223′ developed at the anode of the laser diode D_(L).

As previously described, values of the source capacitor C_(S), theinductor L_(S) and the bypass capacitor C_(BP) may be advantageouslyselected or “tuned” by a designer to meet desired performance criteriaof the pulsed laser diode driver disclosed herein. For example, acapacitance value of the bypass capacitor C_(BP) may be selected basedon a desired pulse width of the current i_(DL) through the laser diodeD_(L). The plot 207 shows the pulse 223 generated when the capacitanceof the bypass capacitor C_(BP) is equal to 1 nF, and a pulse 223″generated when the capacitance of the bypass capacitor C_(BP) is equalto 4 nF. In use cases where a wider pulse, such as the pulse 223″, isdesired, the source voltage V_(S) may be raised accordingly.Additionally, in some embodiments, the width of the de-asserted portionof the bypass switch gate driver signal GATE_(BP) 220 is widened toaccommodate a wider pulse.

FIG. 3 illustrates a portion of an example switching sequence 300 foroperation of the pulsed laser diode drivers 101-103 shown in FIGS. 1A-B,in accordance with some embodiments, and as was described with referenceto FIGS. 2A-C. However, the switching sequence 300 is similar to, or thesame as, respective switching sequences related to the operation ofother embodiments of the pulsed laser diode drivers disclosed herein,including but not limited to the pulsed laser diode drivers 401-404,501-504, 601-604, 701-705, 801-802, and 901-902.

At a precharge step 301, the bypass switch M_(BP) and the laser diodeswitch M_(DL) are off (i.e., not conducting). During the precharge step301, the source capacitor C_(S) is charged through the source resistorR_(S). At a preflux step 302, the bypass switch M_(BP) and the laserdiode switch M_(DL) are transitioned to an ON-state, thereby allowingthe current i_(LS) to flow through the inductor L_(S) to store energy inthe form of magnetic flux at the inductor L_(S). Even though both of theswitches (M_(DL), M_(BP)) are in an ON-state at the preflux step 302,the bypass path through the bypass switch M_(BP) will carry all of thecurrent i_(LS) because a bandgap voltage of the laser diode D_(L) needsto be overcome to allow current to flow through the laser diode D_(L).

In some embodiments, the laser diode switch M_(DL) is transitioned to anON-state after the bypass switch M_(BP) is transitioned to an ON-state.At a pulse generation step 303, the bypass switch M_(BP) is transitionedto an OFF-state while the laser diode switch M_(DL) is maintained in anON-state, thereby generating the high-current pulse through the laserdiode D_(L). When the bypass switch M_(BP) is transitioned to theOFF-state, voltage at the anode of the laser diode D_(L) rises quickly,until the bandgap voltage of the laser diode D_(L) is overcome and thelaser diode D_(L) begins to conduct current. Because of a resonantcircuit formed by the bypass capacitor C_(BP) and the parasiticinductance L_(DL) of the laser diode D_(L), the voltage formed at theanode of the laser diode D_(L) will advantageously rise as high asnecessary to overcome the bandgap voltage of the laser diode D_(L) andwill generally be higher than the source voltage V_(S).

At a discharge step 304, the bypass switch M_(BP) and the laser diodeswitch M_(DL) are maintained in an ON-state to drain charge stored atthe source capacitor C_(S), thereby reducing the current i_(DL) throughthe parasitic inductance L_(DL) to advantageously eliminate a highvoltage spike at the anode of the laser diode D_(L) when the laser diodeswitch M_(DL) is transitioned to an OFF-state. At step 305, the bypassswitch M_(BP) and the laser diode switch M_(DL) are transitioned to anOFF-state, thereby returning to the precharge state at step 301. Becausethe source voltage V_(S) at the source capacitor C_(S) is completelydischarged at the end of the discharge step 304, there is very littlecurrent through the laser diode D_(L). Thus, there is advantageouslyvery little overshoot when the switches M_(DL), M_(BP) are transitionedto the OFF-state at step 305, thereby preventing damage to the laserdiode D_(L) and the switches M_(DL), M_(BP). The time interval of theoverall pulse and bypass signals is selected, in some embodiments, suchthat the source capacitor C_(S) is fully discharged before the switchesM_(DL), M_(BP) are transitioned to the OFF-state at step 305.

Other topologies of pulsed laser drivers, having the same or similaradvantages and having similar operation as that of the pulsed laserdiode drivers 101-103, are disclosed below. The example topologiesdisclosed herein are not an exhaustive list of possible topologies thathave the same or similar advantages and similar operation as that of thepulsed laser diode drivers 101-103. For example, one of skill in the artwill appreciate that some modifications can be made while still adheringto the general principle of operation disclosed herein. Suchmodifications include placement of the bypass capacitor C_(BP),component values, and the addition of serially connected components thatprovide a DC current path.

FIGS. 4A-D are simplified circuit schematics of pulsed laser diodedrivers 401-404 of a second general topology that is configured to drivetwo or more laser diodes in a common anode arrangement, in accordancewith some embodiments. The pulsed laser diode drivers 401-404 eachgenerally include the source resistor R_(S), the source capacitor C_(S),the damping resistor R_(Damp), the inductor L_(S), the bypass capacitorC_(BP), two or more laser diodes D_(L) ¹-D_(L) ^(n), and the bypassswitch M_(BP). The pulsed laser diode drivers 401-402 each include twoor more laser diode switches M_(DL) ¹-M_(DL) ^(n), whereas the pulsedlaser diode drivers 403-404 include a single laser diode switch M_(DL)¹.

Also shown is the controller 120, nodes 410, 412, respective parasiticinductances L_(DL) ¹-L_(DL) ^(n) of the laser diodes DL_(L) ¹-D_(L)^(n), the DC input voltage V_(in), the source voltage V_(S) at thesource capacitor C_(S), the current i_(LS) through the inductor L_(S),respective currents i_(DL) ¹-i_(DL) ^(n) through the laser diodes D_(L)¹-D_(L) ^(n), and the bypass switch gate driver signal GATE_(BP). Thepulsed laser diode drivers 401-402 each utilize respective laser diodeswitch gate driver signals GATE_(DL) ¹-GATE_(DL) ^(n), whereas thepulsed laser diode drivers 403-404 use a single laser diode switch gatedriver signal GATE_(DL) ¹. Electrical connections of the pulsed laserdiode drivers 401-404 are similar to, or the same as, those describedwith respect to the pulsed laser diode drivers 101-103. Topologies ofthe pulsed laser diode drivers 401-404 vary with respect to theplacement of the bypass capacitor C_(BP).

As shown in the simplified circuit schematics of the pulsed laser diodedriver 401 of FIG. 4A and the pulsed laser diode driver 404 of FIG. 4D,in some embodiments the first terminal of the bypass capacitor C_(BP) isdirectly electrically connected to the second terminal of the inductorL_(S) and to the anodes of the laser diodes D_(L) ¹-D_(L) ^(n). In suchembodiments, the second terminal of the bypass capacitor C_(BP) isdirectly electrically connected to the bias voltage node. As shown inthe simplified circuit schematic of the pulsed laser diode drivers402-403 of FIGS. 4B-C, in some embodiments the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to the respective anodes of the laserdiodes D_(L) ¹-D_(L) ^(n). In such embodiments, the second terminal ofthe bypass capacitor C_(BP) is directly electrically connected to thesecond terminal of the source capacitor C_(S) and to the first terminalof the damping resistor R_(Damp). In some embodiments, values of the DCinput voltage V_(in), inductance of the inductor L_(S), capacitance ofthe source capacitor C_(S), resistance of the damping resistor R_(Damp),and capacitance of the bypass capacitor C_(BP) are similar to, or thesame as, those respective values as described with reference to thepulsed laser diode drivers 101-103. However, the values of the DC inputvoltage V_(in), inductance of the inductor L_(S), capacitance of thesource capacitor C_(S), resistance of the damping resistor R_(Damp), andcapacitance of the bypass capacitor C_(BP) can advantageously beselected to achieve desired operation of the pulsed laser diode drivers401-404 (e.g., a charge time, a pulse width, a pulse voltage, a pulsecurrent level). Operation of the pulsed laser diode drivers 401-404 issimilar to, or the same as, operation of the pulsed laser diode drivers101-103 as explained in detail with respect to the simplified plots201-206 of FIGS. 2A-D, as well as the example switching sequence 300shown in FIG. 3.

In some embodiments, the controller 120 is configured to determine howmany of the laser diodes D_(L) ¹-D_(L) ^(n) are enabled simultaneouslyand to adjust a voltage level of the DC input voltage V_(in) inaccordance with that determination to supply a required amount ofcurrent (e.g., using a digitally adjustable voltage source (describedbelow) controlled by a digital control signal from the controller 120).

FIGS. 5A-D are simplified circuit schematics of pulsed laser diodedrivers 501-504 of a third general topology that is configured to drivea laser diode using a high-side switch, in accordance with someembodiments. The pulsed laser diode drivers 501-504 each generallyinclude the source resistor R_(S), the source capacitor C_(S), thedamping resistor R_(Damp), the inductor L_(S), the bypass capacitorC_(BP), the laser diode D_(L), the bypass switch M_(BP), and the laserdiode switch M_(DL). The laser diode switch M_(DL) is configured as ahigh-side switch.

Also shown is the controller 120, nodes 510, 512, the parasiticinductance L_(DL) of the laser diode D_(L), the DC input voltage V_(in),the source voltage V_(S) at the source capacitor C_(S), the currenti_(LS) through the inductor L_(S), the current i_(DL) through the laserdiode D_(L), the bypass switch gate driver signal GATE_(BP), and thelaser diode switch gate driver signal GATE_(DL). Most of the electricalconnections of the pulsed laser diode drivers 501-504 are similar to, orthe same as, those described with respect to the pulsed laser diodedrivers 101-103. However, in contrast to the low-side configuration ofthe pulsed laser diode drivers 101-103, the drain node of the laserdiode switch M_(DL) is directly electrically connected to the secondterminal of the inductor L_(S) and to the drain node of the bypassswitch M_(BP). The source node of the laser diode switch M_(DL) isdirectly electrically connected to the anode of the laser diode D_(L),and the cathode of the laser diode D_(L) is directly electricallyconnected to the bias voltage node. Topologies of the pulsed laser diodedrivers 501-504 vary with respect to placement of the bypass capacitorC_(BP).

As shown in the simplified circuit schematic of the pulsed laser diodedriver 501 of FIG. 5A, in some embodiments the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to the drain node of the laser diodeswitch M_(DL). In such embodiments, the second terminal of the bypasscapacitor C_(BP) is directly electrically connected to the bias voltagenode. As shown in the simplified circuit schematic of the pulsed laserdiode driver 502 of FIG. 5B, in some embodiments the first terminal ofthe bypass capacitor C_(BP) is directly electrically connected to thesource node of the laser diode switch M_(DL) and to the anode of thelaser diode D_(L). In such embodiments, the second terminal of thebypass capacitor C_(BP) is directly electrically connected to the biasvoltage node. As shown in the simplified circuit schematic of the pulsedlaser diode driver 503 of FIG. 5C, in some embodiments the firstterminal of the bypass capacitor C_(BP) is directly electricallyconnected to the second terminal of the inductor L_(S), to the drainnode of the bypass switch M_(BP), and to the drain node of the laserdiode switch M_(DL). In such embodiments, the second terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the source capacitor C_(S) and to the first terminal of thedamping resistor R_(Damp). As shown in the simplified circuit schematicof the pulsed laser diode driver 504 of FIG. 5D, in some embodiments thefirst terminal of the bypass capacitor C_(BP) is directly electricallyconnected to the source node of the laser diode switch M_(DL) and theanode of the laser diode D_(L). In such embodiments, the second terminalof the bypass capacitor C_(BP) is directly electrically connected to thesecond terminal of the source capacitor C_(S) and to the first terminalof the damping resistor R_(Damp).

FIGS. 6A-D are simplified circuit schematics of pulsed laser diodedrivers 601-604 of a fourth general topology that is configured to drivetwo or more laser diodes in a common cathode configuration using ahigh-side switch, in accordance with some embodiments. The pulsed laserdiode drivers 601-604 each generally include the source resistor R_(S),the source capacitor C_(S), the damping resistor R_(Damp), the inductorL_(S), the bypass capacitor C_(BP), the bypass switch M_(BP), two ormore laser diodes D_(L) ¹-D_(L) ^(n), and two or more respective laserdiode switches M_(DL) ¹-M_(DL) ^(n).

Also shown is the controller 120, nodes 610, 612, 614, respectiveparasitic inductances L_(DL) ¹-L_(DL) ^(n) of the laser diodes D_(L)¹-D_(L) ^(n), the DC input voltage V_(in), the source voltage V_(S) atthe source capacitor C_(S), the current i_(LS) through the inductorL_(S), respective currents i_(DL) ¹-i_(DL) ^(n) through the laser diodesD_(L) ¹-D_(L) ^(n), the bypass switch gate driver signal GATE_(BP), andrespective laser diode switch gate driver signals GATE_(DL) ¹-GATE_(DL)^(n) of the laser diode switches M_(DL) ¹-M_(DL) ^(n).

Most of the electrical connections of the pulsed laser diode drivers601-604 are similar to, or are the same as, those described with respectto the pulsed laser diode drivers 501-504. However, topologies of thepulsed laser diode drivers 601-604 vary from one another with respect toplacement of the bypass capacitor C_(BP).

As shown in the simplified circuit schematic of the pulsed laser diodedriver 601 of FIG. 6A, in some embodiments the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to respective drain nodes of thelaser diode switches M_(DL) ¹-M_(DL) ^(n) and the bypass switch M_(BP).In such embodiments, the second terminal of the bypass capacitor C_(BP)is directly electrically connected to the bias voltage node. As shown inthe simplified circuit schematic of the pulsed laser diode driver 602 ofFIG. 6B, in some embodiments the first terminal of the bypass capacitorC_(BP) is directly electrically connected to the source node of any ofthe laser diode switches (M_(DL) ^(n) is shown) and to the anode of thelaser diode coupled to that laser diode switch (D_(L) ^(n) is shown). Insuch embodiments, the second terminal of the bypass capacitor C_(BP) isdirectly electrically connected to the bias voltage node. In someembodiments, multiple bypass capacitors C_(BP) are be used, each of thebypass capacitors being connected across a respective laser diode. Asshown in the simplified circuit schematic of the pulsed laser diodedriver 603 of FIG. 6C, in some embodiments the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to respective drain nodes of thelaser diode switches M_(DL) ¹-M_(DL) ^(n) and the bypass switch M_(BP).In such embodiments, the second terminal of the bypass capacitor C_(BP)is directly electrically connected to the second terminal of the sourcecapacitor C_(S) and to the first terminal of the damping resistorR_(Damp). As shown in the simplified circuit schematic of the pulsedlaser diode driver 604 of FIG. 6D, in some embodiments the firstterminal of the bypass capacitor C_(BP) is directly electricallyconnected to the source node of any of the laser diode switches (M_(DL)¹ is shown) and to the anode of the laser diode coupled to that laserdiode switch (D_(L) ¹ is shown). In such embodiments, the secondterminal of the bypass capacitor C_(BP) is directly electricallyconnected to the second terminal of the source capacitor C_(S) and tothe first terminal of the damping resistor R_(Damp). In someembodiments, multiple bypass capacitors C_(BP) are be used, each of thebypass capacitors C_(BP) having a first terminal that is directlyelectrically connected to a respective anode of each laser diode and asecond terminal that is directly electrically connected to the secondterminal of the source capacitor C_(S) and to the first terminal of thedamping resistor R_(S).

In some embodiments, the controller 120 is operable to determine howmany of the laser diodes D_(L) ¹-D_(L) ^(n) are enabled simultaneouslyand to adjust a voltage level of the DC input voltage V_(in) inaccordance with that determination to supply a required amount ofcurrent (e.g., using a digitally adjustable voltage source (describedbelow) controlled by a digital control signal from the controller 120).

FIGS. 7A-E are simplified circuit schematics of pulsed laser diodedrivers 701-705 of a fifth general topology that is configured to drivea laser diode using a half-bridge configuration, in accordance with someembodiments. The pulsed laser diode drivers 701-704 each generallyinclude the source resistor R_(S), the source capacitor C_(S), thedamping resistor R_(Damp), the inductor L_(S), the bypass capacitorC_(BP), the bypass switch M_(BP), the laser diode D_(L), and the laserdiode switch M_(DL). The pulsed laser diode driver 705 additionallyincludes two or more laser diodes D_(L) ¹-D_(L) ^(n), rather than thesingle laser diode D_(L), each of the two or more laser diodes D_(L)¹-D_(L) ^(n) having a respective parasitic inductance L_(DL) ¹-L_(DL)^(n), and respective current representation i_(DL) ¹-i_(DL) ^(n).However, the pulsed laser diode driver 705 lacks independent control ofthe two or more laser diodes D_(L) ¹-D_(L) ^(n).

Also shown is the controller 120, nodes 710, 712, the parasiticinductance L_(DL) of the laser diode D_(L), the DC input voltage V_(in),the source voltage V_(S) at the source capacitor C_(S), the currenti_(LS) through the inductor L_(S), the current i_(DL) through the laserdiode D_(L), the currents i_(DL) ¹-i_(DL) ^(n) through the two or morelaser diodes D_(L) ¹-D_(L) ^(n), the bypass switch gate driver signalGATE_(BP), and the laser diode switch gate driver signal GATE_(DL) ofthe laser diode switch M_(DL).

Most of the electrical connections of the pulsed laser diode drivers701-704 are similar to, or the same as those described with respect tothe pulsed laser diode drivers 501-503. However, in contrast to thehigh-side configuration of the pulsed laser diode drivers 501-503, thedrain node of the bypass switch M_(BP) is directly electricallyconnected to the source node of the laser diode switch M_(DL) and to theanode of the laser diode D_(L). The source node of the bypass switchM_(BP) is directly electrically connected to the bias voltage node.Thus, as shown in the simplified circuit schematics of the pulsed laserdiode drivers 701-704, the laser diode D_(L) may be driven by thehalf-bridge configuration of the bypass switch M_(BP) and the laserdiode switch M_(DL). Topologies of the pulsed laser diode drivers701-704 vary with respect to placement of the bypass capacitor C_(BP).

As shown in the simplified circuit schematic of the pulsed laser diodedriver 701 of FIG. 7A, in some embodiments the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S) and to the drain node of the laser diodeswitch M_(DL). In such embodiments, the second terminal of the bypasscapacitor C_(BP) is electrically connected to the bias voltage node. Asshown in the simplified circuit schematic of the pulsed laser diodedriver 702 of FIG. 7B, in some embodiments the first terminal of thebypass capacitor C_(BP) is directly electrically connected to the sourcenode of the laser diode switch M_(DL), to the drain node of the bypassswitch M_(BP), and to the anode of the laser diode D_(L). In suchembodiments, the second terminal of the bypass capacitor C_(BP) isdirectly electrically connected to the bias voltage node. As shown inthe simplified circuit schematic of the pulsed laser diode driver 703 ofFIG. 7C, in some embodiments the first terminal of the bypass capacitorC_(BP) is directly electrically connected to the second terminal of theinductor L_(S) and to the drain node of the laser diode switch M_(DL).In such embodiments, the second terminal of the bypass capacitor C_(BP)is directly electrically connected to the second terminal of the sourcecapacitor C_(S) and to the first terminal of the damping resistorR_(Damp). As shown in the simplified circuit schematic of the pulsedlaser diode driver 704 of FIG. 7D, in some embodiments the firstterminal of the bypass capacitor C_(BP) is directly electricallyconnected to the source node of the laser diode switch M_(DL), the drainnode of the bypass switch M_(BP), and the anode of the laser diodeD_(L). In such embodiments, the second terminal of the bypass capacitorC_(BP) is directly electrically connected to the second terminal of thesource capacitor C_(S) and to the first terminal of the damping resistorR_(Damp).

As shown in the simplified circuit schematic of the pulsed laser diodedriver 705 of FIG. 7E, two or more laser diodes D_(L) ¹-D_(L) ^(n) maybe driven simultaneously by the half-bridge configuration of the bypassswitch M_(BP) and the laser diode switch M_(DL). In the example shown,the first terminal of the bypass capacitor C_(BP) is directlyelectrically connected to the second terminal of the inductor L_(S) andthe second terminal of the bypass capacitor C_(BP) is directlyelectrically connected to the second terminal of the source capacitorC_(S) and to the first terminal of the damping resistor R_(Damp).However, other configurations of the bypass capacitor C_(BP), such asthose described with reference to FIGS. 7A-D may be used.

FIGS. 8A-B are simplified circuit schematics of pulsed laser diodedrivers 801-802 of a sixth general topology that is configured to drivea laser diode using a high-side switch, in accordance with someembodiments. The pulsed laser diode drivers 801-802 generally includethe source resistor R_(S), the source capacitor C_(S), the dampingresistor R_(Damp), the inductor L_(S), the bypass capacitor C_(BP), thelaser diode D_(L), the bypass switch M_(BP), and the laser diode switchM_(DL). Also shown is the controller 120, nodes 810, 812, the respectiveparasitic inductances L_(DL) of the laser diode D_(L), the DC inputvoltage V_(in), the source voltage V_(S) at the source capacitor C_(S),the current i_(LS) through the inductor L_(S), the current i_(DL)through the laser diodes D_(L), the bypass switch gate driver signalGATE_(BP), and the laser diode switch gate driver signal GATE_(DL).Electrical connections of the pulsed laser diode driver 801 are similarto, or the same as those described with respect to the pulsed laserdiode driver 101. The pulsed laser diode drivers 801-802 differ in thatthe drain node of the laser diode switch M_(DL) is directly electricallyconnected to the second terminal of the source resistor R_(S) and to thefirst terminal of the source capacitor C_(S). The source node of thelaser diode switch M_(DL) is directly electrically connected to thefirst terminal of the inductor L_(S). The anode of the laser diode D_(L)is directly electrically connected to the second terminal of theinductor L_(S) and the cathode of the laser diode D_(L) is directlyelectrically connected to the bias voltage node. As shown, the pulsedlaser diode drivers 801-802 are advantageously configured such that thelaser diode switch M_(DL) is electrically connected between the inductorL_(S) and the source capacitor C_(S). As a result, the drain node of thelaser diode switch M_(DL) does not receive a high voltage spikedeveloped at the second terminal of the inductor L_(S) when the bypassswitch M_(BP) is disabled to generate the high-current pulse through thelaser diode D_(L).

The pulsed laser diode drivers 801-802 differ in placement of the bypasscapacitor C_(BP). As shown in FIG. 8A, in some embodiments, the firstterminal of the bypass capacitor C_(BP) is directly electricallyconnected to the second terminal of the inductor L_(S), to the anode ofthe laser diode D_(L), and to the drain node of the bypass switchM_(BP). In such embodiments, the second terminal of the bypass capacitorC_(BP) is directly electrically connected to the bias voltage node. Asshown in FIG. 8B, in some embodiments, the first terminal of the bypasscapacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S), to the anode of the laser diode D_(L),and to the drain node of the bypass switch M_(BP). In such embodiments,the second terminal of the bypass capacitor C_(BP) is directlyelectrically connected to the second terminal of the source capacitorC_(S) and to the first terminal of the damping resistor R_(Damp).

In other embodiments, the respective positions of the inductor L_(S) andthe laser diode switch M_(DL) in either of the pulsed laser diodedrivers 801-802, can be exchanged such that the first terminal of theinductor L_(S) is directly electrically connected to the first terminalof the source capacitor C_(S), and the drain terminal of the laser diodeswitch M_(DL) is directly electrically connected to the second terminalof the inductor L_(S).

FIGS. 9A-B are simplified circuit schematics of pulsed laser diodedrivers 901-902 of a seventh general topology that is configured todrive a laser diode using only a bypass switch, in accordance with someembodiments. The pulsed laser diode drivers 901-902 generally includethe source resistor R_(S), the source capacitor C_(S), the dampingresistor R_(Damp), the inductor L_(S), the bypass capacitor C_(BP), thelaser diode D_(L), and the bypass switch M_(BP). Also shown are nodes910, 912, the respective parasitic inductances L_(DL) of the laser diodeD_(L), the DC input voltage V_(in), the source voltage V_(S) at thesource capacitor C_(S), the current i_(LS) through the inductor L_(S),the current i_(DL) through the laser diodes D_(L), and the bypass switchgate driver signal GATE_(BP). Electrical connections of the pulsed laserdiode drivers 901-902 are similar to, or the same as, those describedwith respect to the pulsed laser diode driver 101. The pulsed laserdiode drivers 901-902 differ in that the laser diode switch M_(DL) iseliminated. The anode of the laser diode D_(L) is directly electricallyconnected to the second terminal of the inductor L_(S) and the cathodeof the laser diode D_(L) is directly electrically connected to the biasvoltage node. In such embodiments, the voltage level of the DC inputvoltage V_(in) is restricted to a voltage level that does not surpassthe forward bias voltage of the laser diode D_(L), thereby maintainingthe laser diode D_(L) in an OFF-state (i.e., not conducting) until avoltage higher than the forward bias voltage is developed at the secondterminal of the inductor L_(S) when current flow through the bypassswitch is momentarily disabled.

The pulsed laser diode drivers 901-902 differ in placement of the bypasscapacitor C_(BP). As shown in FIG. 9A, in some embodiments, the firstterminal of the bypass capacitor C_(BP) is directly electricallyconnected to the second terminal of the inductor L_(S), to the anode ofthe laser diode D_(L), and to the drain node of the bypass switchM_(BP). In such embodiments, the second terminal of the bypass capacitorC_(BP) is directly electrically connected to the bias voltage node. Asshown in FIG. 9B, in some embodiments, the first terminal of the bypasscapacitor C_(BP) is directly electrically connected to the secondterminal of the inductor L_(S), to the anode of the laser diode D_(L),and to the drain node of the bypass switch M_(BP). In such embodiments,the second terminal of the bypass capacitor C_(BP) is directlyelectrically connected to the second terminal of the source capacitorC_(S) and to the first terminal of the damping resistor R_(Damp).

Embodiments of the pulsed laser diode drivers disclosed herein areadditionally or alternatively operable to provide current pulses todevices other than laser diodes. For instance, embodiments of the pulsedlaser diode drivers disclosed herein are operable to provide a currentpulse to a light-emitting diode (i.e., a non-laser LED). Additionally,embodiments of the pulsed laser diode drivers disclosed herein areoperable to provide a current pulse to another circuit or device, havingno laser diode, that is configured to receive a current pulse for apurpose other than emitting light.

In some embodiments, two or more instances of the laser diode driversdisclosed herein are configured to drive respective laser diodes. Forexample, four instances of the pulsed laser diode driver 802 may be usedto drive a laser diode package that includes four laser diodes. In suchan embodiment, each of the laser diodes in the laser diode package isdriven by an instance of the pulsed laser diode driver 802.

FIGS. 10A-10B are simplified circuit schematics of pulsed laser diodedrivers 1002/1004 of an eighth general topology that is configured formulti-channel, individual control of multiple laser diodes, inaccordance with some embodiments. The multi-channel pulsed laser diodedriver 1002 shown in FIG. 10A is configured to independently drive nlaser diodes where n is a number ranging from two to 128 or more. Themulti-channel pulsed laser diode driver 1002 is operable to cause apulse to be emitted from any individual laser diode of the multi-channelpulsed laser diode driver 1002 in isolation, or combined with one ormore other pulses emitted from other laser diodes of the multi-channelpulsed laser diode driver 1002. The multi-channel pulsed laser diodedriver 1002 generally includes n source resistors Rs¹ through Rs^(n), nsource capacitors C_(S) ¹ through C_(S) ^(n), an optional dampingresistor R_(Damp), n inductors Ls¹ through Ls^(n), n bypass switchesM_(BP) ¹ through M_(BP) ^(n), n bypass capacitors C_(BP) ¹ throughC_(BP) ^(n), n laser diodes D_(L) ¹ through D_(L) ^(n), and a laserdiode switch M_(DL), coupled as shown. Also shown is the controller 120discussed above, respective parasitic inductances L_(DL) ¹ throughL_(DL) ^(n) of the laser diodes D_(L) ¹ through D_(L) ^(n), respectivecurrents i_(LS) ¹ through i_(LS) ^(n) of the inductors Ls¹ throughLs^(n), respective currents i_(DL) ¹ through i_(DL) ^(n) of the laserdiodes D_(L) ¹ through D_(L) ^(n), and the DC input voltage V_(in). Thedamping resistor R_(Damp) is used in some embodiments for currentmeasurement purposes and can be omitted by connecting each of the sourcecapacitors C_(S) ¹ through C_(S) ^(n) to ground. In some embodiments,the bypass switches M_(BP) ¹ through M_(BP) ^(n) and the laser diodeswitch M_(DL) are each N-type FET switches and advantageously do notrequire bootstrap circuitry to drive the respective gates of thoseswitches because of their respective low-side configurations.

The source resistor Rs¹, the source capacitor C_(S) ¹, the inductor Ls¹,the bypass switch M_(BP) ¹, the bypass capacitor C_(BP) ¹, and the laserdiode D_(L) ¹ are associated with a first channel of the multi-channelpulsed laser diode driver 1002. Similarly, the source resistor Rs^(n),the source capacitor C_(S) ^(n), the inductor Ls^(n), the bypass switchM_(BP) ^(n), the bypass capacitor C_(BP) ^(n), and the laser diode D_(L)^(n) are associated with an n^(th) channel of the multi-channel pulsedlaser diode driver 1002, where n is a number greater than one (e.g.,two, three, four, eight, 16, 32, 64, 128, etc.). By controlling (e.g.,by the controller 120) respective switch timings (i.e., an on/offduration) of the bypass switches M_(BP) ¹ through M_(BP) ^(n) inconjunction with controlling a switch timing of the laser diode switchM_(DL) each of the laser diodes D_(L) ¹ through D_(L) ^(n) areadvantageously independently controlled. Operation of each channel ofthe multi-channel pulsed laser diode driver 1002 is similar to, or thesame as, operation of the pulsed laser diode driver 101 described withreference to FIG. 1A and the switching sequence 300 shown in FIG. 3.Because each of the bypass switches M_(BP) ¹ through M_(BP) ^(n) and thelaser diode switch M_(DL) are configured as low-side switches (i.e., asource node of each aforementioned switch is directly electricallyconnected to ground), a gate control signal of those switches does notneed to be level-shifted by bootstrap circuitry, thereby advantageouslysimplifying the design and reducing the cost of the multi-channel pulsedlaser diode driver 1002 as compared to a laser diode driver circuit thatrequires bootstrap circuitry.

An example embodiment of a four-channel (i.e., n=4) multi-channel pulsedlaser diode driver 1004 is shown in FIG. 10B. The multi-channel pulsedlaser diode driver 1004 is operable to independently drive four laserdiodes. That is, the multi-channel pulsed laser diode driver 1004 isoperable to cause a pulse to be emitted from any individual laser diodeof the multi-channel pulsed laser diode driver 1004 in isolation, orcombined with one or more other pulses emitted from other laser diodesof the multi-channel pulsed laser diode driver 1004. The multi-channelpulsed laser diode driver 1004 generally includes four source resistorsRs¹ through Rs⁴, four source capacitors Cs¹ through Cs⁴, the optionaldamping resistor R_(Damp), four inductors Ls¹ through Ls⁴, four bypassswitches M_(BP) ¹ through M_(BP) ⁴, four bypass capacitors C_(BP) ¹through C_(BP) ⁴, four laser diodes D_(L) ¹ through D_(L) ⁴, and thelaser diode switch M_(DL), directly electrically connected as shown.Also shown is the controller 120, respective parasitic inductancesL_(DL) ¹ through L_(DL) ⁴ of the laser diodes D_(L) ¹ through D_(L) ⁴,the DC input voltage V_(in), nodes 1011 through 1014, and nodes 1021through 1024. The damping resistor R_(Damp) is used in some embodimentsfor current measurement purposes and can be omitted by connecting eachof the source capacitors C_(S) ¹ through C_(S) ⁴ to ground. In someembodiments, the bypass capacitors C_(BP) ¹ through C_(BP) ⁴ areconnected to the cathodes of the laser diodes D_(L) ¹ through D_(L) ⁴.In some embodiments, the bypass switches M_(BP) ¹ through M_(BP) ⁴ andthe laser diode switch M_(DL) are each N-type FET switches andadvantageously do not require boot-strap circuitry to drive therespective gates of those switches as described above.

The source resistor Rs¹, the source capacitor C_(S) ¹, the inductor Ls¹,the bypass switch M_(BP) ¹, the bypass capacitor C_(BP) ¹, and the laserdiode D_(L) ¹ are associated with a first channel of the multi-channelpulsed laser diode driver 1004; the source resistor Rs², the sourcecapacitor C_(S) ², the inductor Ls², the bypass switch M_(BP) ², thebypass capacitor C_(BP) ², and the laser diode D_(L) ² are associatedwith a second channel of the multi-channel pulsed laser diode driver1004; the source resistor Rs³, the source capacitor C_(S) ³, theinductor Ls³, the bypass switch M_(BP) ³, the bypass capacitor C_(BP) ³,and the laser diode D_(L) ³ are associated with a third channel of themulti-channel pulsed laser diode driver 1004, and the source resistorRs⁴, the source capacitor C_(S) ⁴, the inductor Ls⁴, the bypass switchM_(BP) ⁴, the bypass capacitor C_(BP) ⁴, and the laser diode D_(L) ⁴ areassociated with a fourth channel of the multi-channel pulsed laser diodedriver 1004. The laser diode switch M_(DL) is associated with each ofthe channels of the multi-channel pulsed laser diode driver 1004.

As described above, each channel of the multi-channel pulsed laser diodedriver 1004 has an associated source resistor, source capacitor,inductor, bypass switch, bypass capacitor, and laser diode. Bycontrolling (e.g., by the controller 120) respective switch timings(i.e., an on/off duration) of the bypass switches M_(BP) ¹ throughM_(BP) ⁴ in conjunction with controlling a switch timing of the laserdiode switch M_(DL), each of the laser diodes D_(L) ¹ through D_(L) ⁴ isadvantageously independently controlled.

Operation of each channel of the multi-channel pulsed laser diode driver1004 is similar to, or the same as operation of the pulsed laser diodedriver 101 described with reference to FIG. 1A and the switchingsequence 300 shown in FIG. 3. A channel of the multi-channel pulsedlaser diode driver 1004 is selected for output by turning that channel'sbypass switch off (e.g., by the controller 120) while the laser diodeswitch M_(DL) is off such that the DC input voltage V_(in) charges thatchannel's source capacitor to a desired voltage level to store energy inthat source capacitor (e.g., step 301 of FIG. 3). After the desiredvoltage level is reached at the source capacitor, a selected channel'sbypass switch is turned on (e.g., by the controller 120), such thatcurrent builds in that channel's inductor between that channel's bypassswitch and that channel's source capacitor (e.g., step 302 of FIG. 3).If that channel's bypass switch is thereafter turned off for a shorttime and the laser diode switch M_(DL) is turned on, that channel'sinductor current will resonate with the anode capacitance of thatchannel's laser diode, thereby creating a voltage across that channel'slaser diode that is higher than the DC input voltage V_(in) and thedeveloped current will be forced to flow through that channel's laserdiode (e.g., step 303 of FIG. 3) to emit a laser pulse. In someembodiments, a discharge sequence similar to step 304 of FIG. 3 isperformed, whereby both that channel's bypass switch and the laser diodeswitch M_(DL) are turned on may then follow. By sequentially selectingeach channel of the multi-channel laser diode driver 1004, thatchannel's laser diode can be independently pulsed. A channel of themulti-channel pulsed laser diode driver 1004 is unselected for output byleaving that channel's bypass switch on (e.g., by the controller 120)through each of the steps 301 through 305 shown in FIG. 3, therebypreventing the DC input voltage V_(in) from charging that channel'ssource capacitor.

Simplified example waveforms 1102 of signals related to the operation ofthe multi-channel pulsed laser diode driver 1004 are shown in FIG. 11,in accordance with some embodiments. Also shown is a legend 1101 andexpanded regions of interest 1104, 1106, 1108, and 1110 of the waveforms1102.

As indicated by the legend 1101, the simplified waveforms 1102 of FIG.11 include a laser diode switch gate driver signal Gate_(DL), a firstbypass switch gate driver signal Gate_(BP) ¹, a second bypass switchgate driver signal Gate_(BP) ², a third bypass switch gate driver signalGate_(BP) ³ and a fourth bypass switch gate driver signal Gate_(BP) ⁴over a 20 μs duration. With reference to FIG. 10B, the laser diodeswitch gate driver signal Gate_(DL) is operable to control the laserdiode switch M_(DL), the first bypass switch gate driver signalGate_(BP) ¹ is operable to control the bypass switch M_(BP) ¹, thesecond bypass switch gate driver signal Gate_(BP) ² is operable tocontrol the bypass switch M_(BP) ², the third bypass switch gate driversignal Gate_(BP) ³ is operable to control the bypass switch M_(BP) ³,and the fourth bypass switch gate driver signal Gate_(BP) ⁴ is operableto control the bypass switch M_(BP) ⁴.

Each of the expanded regions of interest 1104, 1106, 1108, and 1110illustrate a pre-flux interval of a selected channel during which aninductor current of that channel's inductor is ramping up, a very shortpulse interval during which current through that channel's inductor isdirected through that channel's laser diode, and a discharge interval inaccordance with steps 301 through 305 described with reference to FIG.3. Per the description above, the region of interest 1104 illustratespulse generation for the first channel (i.e., laser diode D_(L) ¹) ofthe multi-channel laser diode driver 1004, the region of interest 1106illustrates pulse generation for the second channel (i.e., laser diodeD_(L) ²) of the multi-channel laser diode driver 1004, the region ofinterest 1108 illustrates pulse generation for the third channel (i.e.,laser diode D_(L) ³) of the multi-channel laser diode driver 1004, andthe region of interest 1110 illustrates pulse generation for the fourthchannel (i.e., laser diode D_(L) ²) of the multi-channel laser diodedriver 1004.

Additional simplified example waveforms 1202 of signals related to theoperation of the multi-channel pulsed laser diode driver 1004 of FIG.10B are shown in FIG. 12. The simplified example waveforms includewaveforms 1211 through 1214 illustrating respective anode voltages ofthe laser diodes D_(L) ¹ through D_(L) ⁴ at the nodes 1011 through 1014,and waveforms 1221 through 1224 illustrating respective voltages of thesource capacitor C_(S) ¹ through C_(S) ⁴ at the nodes 1021 through 1024.Also shown are waveforms 1231 through 1234 which illustrate when arespective channel of the multi-channel pulsed laser diode driver 1004is enabled.

As shown, when a first channel of the multi-channel pulsed laser diodedriver 1004 is enabled (illustrated by waveform 1231), an anode voltage1211 at node 1011 of the laser diode D_(L) ¹ rises in conjunction with arising voltage at node 1021 of the source capacitor C_(S) ¹. Uponenabling the laser diode switch M_(DL) and momentarily disabling thebypass switch M_(BP) ¹, current flows through the laser diode D_(L) ¹,thereby emitting a laser pulse as described above. Similarly, when asecond channel of the multi-channel pulsed laser diode driver 1004 isenabled (illustrated by waveform 1232), an anode voltage 1212 at node1012 of the laser diode D_(L) ² rises in conjunction with a risingvoltage at node 1022 of the source capacitor C_(S) ². Upon enabling thelaser diode switch M_(DL) and momentarily disabling the bypass switchM_(BP) ², current flows through the laser diode D_(L) ², therebyemitting a laser pulse as described above. Operation of the third andfourth channels of the multi-channel laser diode driver 1004 aresimilar.

A repetition rate of the multi-channel pulsed laser diode driver 1004,as well as each of the pulsed laser diode drivers described above, islimited by a charging time of each channel's source capacitor. Thepulsed laser diode drivers described above create narrow (e.g., 1-5nsec) high-current pulses (e.g., 40 amp) through a driven laser diode.The instantaneous power in the driven laser diode is therefore high(e.g., in the order of hundreds of watts). However, for manyapplications (e.g., Lidar), the duty cycle of the pulse is generally0.01% or less to limit the total power dissipated in the laser diodewhich results in an upper limit to a repetition rate. In conventionallaser diode driver applications, a resistor is used to charge storage(i.e., source) capacitors during each cycle. In such conventionalsolutions, an RC time constant of such charging circuits is typicallynot an issue because the duty cycle is so low. However, for applicationsthat require a high repetition rate for laser pulses, the RC timeconstant of conventional charging circuits creates an undesirablelimitation. In any of the embodiments disclosed herein, each sourceresistor of a given pulsed laser diode driver may be advantageouslyreplaced by an actively controlled source switch that quickly charges anassociated source capacitor. Activation of the source switch issynchronized with switching the one or more bypass switches and one ormore laser diode switches of a given pulsed laser diode driver such thatthe source switch is enabled prior to a laser diode pulse generationinterval. FIG. 13A through FIG. 13I provide examples of previouslydescribed laser diode drivers in which the respective source resistorR_(S) has been replaced by an actively controlled source switch M_(S) torapidly charge the respective source capacitor C_(S). In someembodiments, the actively controlled source switch is implemented as aP-type switch which advantageously does not require bootstrap circuitry.Respective actively controlled source switches M_(S) shown in FIG. 13Athrough FIG. 13I are activated only during a pre-charge step (i.e.,during step 301 as described with reference to FIG. 3), and thus priorto a pre-flux step (i.e., prior to step 302 as described with referenceto FIG. 3).

FIG. 13A shows a first example embodiment of a pulsed laser diode driver1301 having all of the components, signals, and nodes described abovewith reference to the pulsed laser diode driver 101 of FIG. 1A, with theexception of the source resistor R_(S) of FIG. 1A which hasadvantageously been replaced in FIG. 13A by an actively controlled(e.g., by the controller 120 using gate control signal GATE_(S)) sourceswitch M_(S) to rapidly charge the source capacitor C_(S). In otherexample embodiments (not shown), the respective source resistors Rs ofthe pulsed laser diode driver 102 of FIG. 1B and the pulsed laser diodedriver 103 of FIG. 1C are similarly replaced by a respective activelycontrolled source switch to rapidly charge the respective sourcecapacitors C_(S) of the laser diode drivers 102/103.

FIG. 13B shows a second example embodiment of a pulsed laser diodedriver 1302 having all of the components, signals, and nodes describedabove with reference to the pulsed laser diode driver 401 of FIG. 4A,with the exception of the source resistor Rs of FIG. 4A which hasadvantageously been replaced in FIG. 13B by an actively controlled(e.g., by the controller 120 using gate control signal GATE_(S)) sourceswitch M_(S) to rapidly charge the source capacitor C_(S). In otherexample embodiments (not shown), the respective source resistors Rs ofthe pulsed laser diode driver 402 of FIG. 4B, the pulsed laser diodedriver 403 of FIG. 4C, and the pulsed laser diode driver 404 of FIG. 4Dare similarly replaced by a respective actively controlled source switchto rapidly charge the respective source capacitors C_(S) of the laserdiode drivers 402/403/404.

FIG. 13C shows a third example embodiment of a pulsed laser diode driver1303 having all of the components, signals, and nodes described abovewith reference to the pulsed laser diode driver 501 of FIG. 5A, with theexception of the source resistor Rs of FIG. 5A which has advantageouslybeen replaced in FIG. 13C by an actively controlled (e.g., by thecontroller 120 using gate control signal GATE_(S)) source switch M_(S)to rapidly charge the source capacitor C_(S). In other exampleembodiments (not shown), the respective source resistors Rs of thepulsed laser diode driver 502 of FIG. 5B, the pulsed laser diode driver503 of FIG. 5C, and the pulsed laser diode driver 504 of FIG. 5D aresimilarly replaced by a respective actively controlled source switch torapidly charge the respective source capacitors C_(S) of the laser diodedrivers 502/503/504.

FIG. 13D shows a fourth example embodiment of a pulsed laser diodedriver 1304 having all of the components, signals, and nodes describedabove with reference to the pulsed laser diode driver 601 of FIG. 6A,with the exception of the source resistor Rs of FIG. 6A which hasadvantageously been replaced in FIG. 13D by an actively controlled(e.g., by the controller 120 using gate control signal GATE_(S)) sourceswitch M_(S) to rapidly charge the source capacitor C_(S). In otherexample embodiments (not shown), the respective source resistors Rs ofthe pulsed laser diode driver 602 of FIG. 6B, the pulsed laser diodedriver 603 of FIG. 6C, and the pulsed laser diode driver 604 of FIG. 6Dare similarly replaced by a respective actively controlled source switchto rapidly charge the respective source capacitors C_(S) of the laserdiode drivers 602/603/604.

FIG. 13E shows a fifth example embodiment of a pulsed laser diode driver1305 having all of the components, signals, and nodes described abovewith reference to the pulsed laser diode driver 701 of FIG. 7A, with theexception of the source resistor Rs of FIG. 7A which has advantageouslybeen replaced in FIG. 13E by an actively controlled (e.g., by thecontroller 120 using gate control signal GATE_(S)) source switch M_(S)to rapidly charge the source capacitor C_(S). In other exampleembodiments (not shown), the respective source resistors Rs of thepulsed laser diode driver 702 of FIG. 7B, the pulsed laser diode driver703 of FIG. 7C, the pulsed laser diode driver 704 of FIG. 7D, and thepulsed laser diode driver 705 of FIG. 7E are similarly replaced by arespective actively controlled source switch to rapidly charge therespective source capacitors C_(S) of the laser diode drivers702/703/704/705.

FIG. 13F shows a sixth example embodiment of a pulsed laser diode driver1306 having all of the components, signals, and nodes described abovewith reference to the pulsed laser diode driver 801 of FIG. 8A, with theexception of the source resistor Rs of FIG. 8A which has advantageouslybeen replaced in FIG. 13F by an actively controlled (e.g., by thecontroller 120 using gate control signal GATE_(S)) source switch M_(S)to rapidly charge the source capacitor C_(S). In other exampleembodiments (not shown), the source resistor Rs of the pulsed laserdiode driver 802 of FIG. 8B is similarly replaced by an activelycontrolled source switch to rapidly charge the source capacitor C_(S) ofthe pulsed laser diode driver 802.

FIG. 13G shows a seventh example embodiment of a pulsed laser diodedriver 1307 having all of the components, signals, and nodes describedabove with reference to the pulsed laser diode driver 901 of FIG. 9A,with the exception of the source resistor Rs of FIG. 9A which hasadvantageously been replaced in FIG. 13G by an actively controlled(e.g., by the controller 120 using gate control signal GATE_(S)) sourceswitch M_(S) to rapidly charge the source capacitor C_(S). In otherexample embodiments (not shown), the source resistor Rs of the laserdiode driver 902 of FIG. 9B is similarly replaced by an activelycontrolled source switch to rapidly charge the source capacitor C_(S) ofthe laser diode driver 902.

FIG. 13H shows an eighth example embodiment of a pulsed laser diodedriver 1308 having all of the components, signals, and nodes describedabove with reference to the multi-channel pulsed laser diode driver 1002of FIG. 10A, with the exception of the source resistors R_(S) ¹ thoughR_(S) ^(n) of FIG. 10A which have advantageously been replaced in FIG.13H by respective actively controlled (e.g., by the controller 120 usinggate control signals GATE_(S) ¹ through GATE_(S) ^(n)) source switchesM_(S) ¹ through M_(S) ^(n) to rapidly charge the source capacitors C_(S)¹ through C_(S) ^(n).

FIG. 13I shows a ninth example embodiment of a pulsed laser diode driver1309 having all of the components, signals, and nodes described abovewith reference to the multi-channel pulsed laser diode driver 1004 ofFIG. 10B, with the exception of the source resistors R_(S) ¹ throughR_(S) ⁴ of FIG. 10B which have advantageously been replaced in FIG. 13Iby respective actively controlled (e.g., by the controller 120 usinggate control signals GATE_(S) ¹ through GATE_(S) ⁴) source switchesM_(S) ¹ through M_(S) ⁴ to rapidly charge the source capacitors C_(S) ¹through C_(S) ⁴.

Simplified example waveforms 1402 of signals related to the operation ofthe multi-channel pulsed laser diode driver 1309 of FIG. 13I are shownin FIG. 14, in accordance with some embodiments. The simplified examplewaveforms 1402 include waveforms 1421 through 1424 illustratingrespective voltages across the source capacitor C_(S) ¹ through C_(S) ⁴at nodes 1021 through 1024 of FIG. 13I, respectively. Also shown arewaveforms 1431 through 1434 which illustrate when a respective channelof the multi-channel pulsed laser diode driver 1309 is enabled, a clocksignal 1441, and high-current pulses 1451 through 1455. As shown, themulti-channel pulsed laser diode driver 1309 is operable to emit ahigh-current pulse 1451 through 1455 to drive a respective laser diodeD_(L) ¹ through D_(L) ⁴, a pulse being emitted every 10 μs. The examplesshown in FIGS. 13A-13I are merely select examples of pulsed laser diodedriver circuits configured to advantageously use a source switch (i.e.,M_(S)) for rapid charging of a source capacitor (i.e., C_(S)). In someembodiments, any of the pulsed laser diode drivers 101-103, 401-404,501-504, 601-604, 701-705, 801-802, 901-902, 1002-1004 are configured touse a source switch (i.e., M_(S)) instead of a source resistor (i.e.,R_(S)) to rapidly charge a source capacitor (i.e., C_(S)).

FIG. 15 shows a simplified circuit schematic of a pulsed laser diodedriver 1501 of a ninth general topology, in accordance with someembodiments. The pulsed laser diode driver 1501 generally includes asource switch M_(S), a source capacitor C_(S), a damping resistorR_(Damp), an inductor L_(S), a bypass capacitor C_(BP), a laser diodeD_(L), a bypass switch M_(BP), and a flux switch M_(FLUX). The fluxswitch M_(FLUX) is configured as a low-side switch. Also shown is thecontroller 120, node 110, a parasitic inductance L_(DL) of the laserdiode D_(L), a DC input voltage V_(in), a source voltage V_(S) at thesource capacitor C_(S), a current i_(LS) through the inductor L_(S), acurrent i_(DL) through the laser diode D_(L), a bypass switch gatedriver signal GATE_(BP), and a flux switch gate driver signalGATE_(FLUX).

As shown in FIG. 15, a first terminal of the source switch M_(S) isdirectly electrically connected to the DC input voltage V_(in). In otherembodiments (not shown), the source switch M_(S) may be replaced with asource resistor R_(S). A second terminal of the source switch M_(S) isdirectly electrically connected to a first terminal of the sourcecapacitor C_(S). A second terminal of the source capacitor C_(S) isdirectly electrically connected to a bias voltage node such as ground.The second terminal of the source switch M_(S) is directly electricallyconnected to an anode of the laser diode D_(L), a first terminal of thedamping resistor R_(Damp), a first terminal of the bypass capacitorC_(BP), and a first terminal of the inductor L_(S). A second terminal ofthe damping resistor R_(Damp) is directly electrically connected to afirst terminal of the flux switch M_(FLUX), and a second terminal of theflux switch M_(FLUX) is directly electrically connected to a biasvoltage node such as ground. A cathode of the laser diode D_(L) isdirectly electrically connected to a second terminal of the bypasscapacitor C_(BP), a second terminal of the inductor L_(S), and to afirst terminal of the bypass switch M_(BP). A second terminal of thebypass switch M_(BP) is directly electrically connected to a biasvoltage node such as ground.

The bypass switch M_(BP) is configured to receive the bypass switch gatedriver signal GATE_(BP) at a gate node (e.g., from the controller 120),the bypass switch gate driver signal GATE_(BP) being operable to turnthe bypass switch M_(BP) on or off based on a voltage level of thebypass switch gate driver signal GATE_(BP). The source switch M_(S) isconfigured to receive the source switch gate driver signal GATE_(S) at agate node (e.g., from the controller 120), the source switch gate driversignal GATE_(S) being operable to turn the source switch M_(S) on or offbased on a voltage level of the source switch gate driver signalGATE_(S). Similarly, the flux switch M_(FLUX) is configured to receivethe flux switch gate driver signal GATE_(FLUX) at a gate node (e.g.,from the controller 120), the flux switch gate driver signal GATE_(FLUX)being operable to turn the flux switch M_(FLUX) on or off based on avoltage level of the flux switch gate driver signal GATE_(FLUX). Any orall of the bypass switch M_(BP), the source switch M_(S), and/or theflux switch M_(FLUX) can be implemented as N-type switches or P-typeswitches. In some embodiments, the bypass switch M_(BP), the sourceswitch M_(S), and/or the flux switch M_(FLUX) are implemented asSilicon-based or Silicon-Carbide-based field-effect transistors (FETs).

In some embodiments, the pulsed laser diode driver 1501 is configured toreceive the DC input voltage V_(in) having a voltage range from about10V to 20V, which is advantageously lower than an input voltage used bymany conventional pulsed laser diode drivers. The inductor L_(S) is aphysical component added to the pulsed laser diode driver 1501 (i.e., asopposed to a representation of a parasitic inductance caused bycomponents or interconnections such as bond wires). Similarly, thebypass capacitor C_(BP) is a physical component added to the pulsedlaser diode driver 1501 (i.e., as opposed to a representation of aparasitic capacitance). One advantage of using physical inductor andcapacitor components rather than using parasitic inductances andcapacitances is that values of the inductor L_(S) and the bypasscapacitor C_(BP) can be easily modified by a designer or even anend-user. By comparison, conventional designs that rely on parasiticreactances may require re-design and/or re-layout to change an operatingparameter.

As disclosed herein, values of the DC input voltage V_(in), theinductance of the inductor L_(S), the capacitance of the sourcecapacitor C_(S), the resistance of the damping resistor R_(Damp), andthe capacitance of the bypass capacitor C_(BP) can advantageously beselected (“tuned”) to achieve a desired operation of the pulsed laserdiode driver 1501 (e.g., a charge time, a pulse width, a pulse voltage,a pulse current). For example, a pulse width of the current i_(DL)flowing through the laser diode D_(L) can be tuned by adjusting thecapacitance value of the bypass capacitor C_(BP). A peak current levelof the pulse of current i_(DL) flowing through the laser diode D_(L) canbe tuned by adjusting the source voltage V_(S) on the supply capacitorC_(S). A capacitance value of the source capacitor C_(S) can be tuned toadjust a timing delay of the high-current pulse and an upper range ofthe current i_(DL) through the laser diode D_(L). Resistance values ofthe damping resistor R_(Damp) are dependent on the capacitance value ofthe supply capacitor C_(S) and can be tuned within a range of valuessuch that at a lower resistance, a lower frequency resonance of thepulsed laser diode drivers disclosed herein is underdamped (e.g., atabout R_(Damp)=0.1 Ohm), or is critically damped (e.g., at aboutR_(Damp)=0.4 Ohm). The damping resistor R_(Damp) is operable to preventcurrent of the generated resonant waveform from becoming negative whichcould thereby enable a body diode of the bypass switch M_(BP) or theflux switch M_(FLUX). Although a resulting maximum current level of thecurrent i_(DL) through the laser diode D_(L) is lower for the criticallydamped case, the current level can be easily adjusted by raising thevoltage level of the DC input voltage V_(in).

In some embodiments, the DC input voltage V_(in) is about 15V, theinductance of the inductor L_(S) is about 6 nH, the capacitance of thesource capacitor C_(S) is about 100 nF, the resistance of the dampingresistor R_(Damp) is about 0.1 Ohm, and the capacitance of the bypasscapacitor C_(BP) is about 1 nF. In some embodiments, a voltage at thefirst terminal of the damping resistor R_(Damp) is received by thecontroller 120 to provide an indication of a current flow through thedamping resistor R_(Damp).

Typical resonant driver designs often require a damping resistor tominimize ringing duration. However, the added damping resistor R_(Damp)dissipates power which may lower the overall power efficiency of thedesign as compared to a resonant driver that does not have a dampingresistor. Thus, in some embodiments, the pulsed laser diode driver 1501advantageously allows current to flow through the damping resistorR_(Damp) during portions of a switching sequence (e.g., the switchingsequence 300) in which the damping resistor R_(Damp) critically dampsringing, and prevents current from flowing through the damping resistorR_(Damp) during portions of the switching sequence when the dampingresistor R_(Damp) is not needed to damp ringing. The pulsed laser diodedriver 1501 allows current to flow through the damping resistor R_(Damp)by enabling the flux switch M_(FLUX) and prevents current from flowingthrough the damping resistor R_(Damp) by disabling the flux switchM_(FLUX). Such dynamic control of current flow through the dampingresistor R_(Damp) advantageously increases an overall power efficiencyof the pulsed laser diode driver 1501 as compared to a pulsed laserdiode driver circuit that allows current to flow through a dampingresistor for the entirety of a switching sequence.

During operation, the source capacitor C_(S) is discharged through theinductor L_(S) by the bypass switch M_(BP). This configuration providesa maximum peak current through the laser diode L_(DL) but requires theseries damping resistor R_(Damp) to prevent the waveform from ringingfor a long duration. Until the ringing stops and the voltage and currentare zero, the bypass switch M_(BP) cannot be turned off. Unfortunately,the damping resistor R_(Damp) dissipates power as long as current flowsthrough the damping resistor R_(Damp). Thus, the pulsed laser diodedriver 1501 advantageously provides an optimal power efficiency bypreventing current from flowing through the damping resistor R_(Damp)during an initial precharge step (e.g., step 301 of FIG. 3), a prefluxstep (e.g., step 302 of FIG. 3), and a pulse generation step (e.g., step303 of FIG. 3) of a switching sequence (e.g., the switching sequence 300of FIG. 3). However, current is allowed, by the flux switch M_(FLUX), toflow through the damping resistor R_(Damp) after the high-current pulsehas been generated (e.g., at step 303 of FIG. 3) to remove remainingringing by critically damping the RLC network of the pulsed laser diodedriver 1501.

During the precharge step (e.g., step 301 of FIG. 3), the preflux step(e.g., step 302 of FIG. 3), and the pulse generation step (e.g., step303 of FIG. 3) of the switching sequence (e.g., the switching sequence300 of FIG. 3), the flux switch M_(FLUX) is disabled, thereby creatingan undamped LC network. However, after pulse generation, the flux switchM_(FLUX) is enabled and the damping resistor R_(Damp) creates a parallelRLC network to critically damp ringing and thereby provide a maximumpower efficiency and fast recovery of the pulsed laser diode driver 1501to start a next switching sequence.

For example, FIGS. 16A-16B show simplified plots, 1620 a-b, 1621 a-b,1622 a-b, 1623 a-b, 1624 a-b, and 1625 a-b, of signals related tooperation of the pulsed laser diode driver 1501 shown in FIG. 15, inaccordance with some embodiments. In particular, FIG. 16A illustratesoperation of the pulsed laser diode driver 1501 when a damping resistor(i.e., the damping resistor R_(Damp)) underdamps ringing of the pulsedlaser diode driver 1501. In comparison, FIG. 16B illustrates operationof the pulsed laser diode driver 1501 when a damping resistor (i.e., thedamping resistor R_(Damp)) is used to critically damp ringing of thepulsed laser diode driver 1501.

With reference to FIGS. 16A-16B, the simplified plots illustrate voltageplots of the bypass switch gate driver signal GATE_(BP) 1620 a-b,voltage plots of the flux switch gate driver signal GATE_(FLUX) 1621a-b, current plots of the current i_(LS) through the inductor L_(S) 1622a-b, current plots of the current i_(DL) through the laser diode D_(L)1623 a-b, voltage plots of the source voltage V_(S) 1624 a-b at thesource capacitor C_(S), and voltage and current plots 1625 a-b of avoltage and current source used to establish a plot scale, all over thesame duration of time. Details of these signals are described below. Thevoltage plots of the bypass switch gate driver signal GATE_(BP) 1620 a-band the flux switch gate driver signal GATE_(FLUX) 1621 a-b have beenlevel-shifted for readability, but are, in actuality, low voltageinputs. Additionally, the voltage plots of the bypass switch gate driversignal GATE_(BP) 1620 a-b and the flux switch gate driver signalGATE_(FLUX) 1621 a-b assume that the flux switch M_(FLUX) and the bypassswitch M_(BP) are NFET devices. However, if PFET devices are usedinstead, the polarity of the bypass switch gate driver signal GATE_(BP)1620 a-b and the flux switch gate driver signal GATE_(FLUX) 1621 a-b areinverted.

In the example shown in FIG. 16A, with reference to FIG. 15, aresistance value of 10 Ohms is used for the damping resistor R_(Damp) ofthe pulsed laser diode driver 1501 in which L_(S)=6 nH, and C_(BP)=1 nF,and L_(DL) is about 1 nH. As expected, the waveforms 1622 a and 1624 aare very underdamped as shown by prolonged oscillations (i.e.,“ringing”). As is known in the art, for a parallel RLC circuit, thedamping coefficient d is expressed as:

$\begin{matrix}{{d = {\frac{1}{2R} \times \sqrt{\frac{L}{C}}}}.} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Thus, if a critically damped waveform is desired, an optimal resistanceR value of the damping resistor R_(Damp) can be determined by settingthe damping coefficient d in Equation 1 to a value of d=1 and solvingEquation 1 for R using the values mentioned above. In the example shownin FIG. 16B, a resistance value of 0.175 Ohms is used for the dampingresistor R_(Damp) of the pulsed laser diode driver 1501. As expected,the waveforms 1622 b and 1624 b are thereby critically damped as shownby the absence of prolonged oscillations (i.e., “ringing”).

In some embodiments, the damping resistor R_(Damp) can be eliminated byusing a weak switch having an on-resistance Rdson that is about thedesired resistance value determined using Equation 1. In suchembodiments, if adjustment of the resistance value is desired, asegmented FET can be used to thereby allow the on-resistance Rdson to bemodified to match the damping resistance required.

Additionally, although it would initially appear that placing the sourcecapacitor C_(S) in series with the laser diode D_(L) would raise therequired anode voltage to pulse the laser diode D_(L), the voltage andcurrent of the source capacitor C_(S) are 90-degrees out of phase withone another. As shown by waveforms 1624 a-b, because the current pulse(i.e., 1623 a-b) through the laser diode D_(L) is advantageously alignedwith a peak current amplitude, voltage at the source capacitor C_(S) atthat time is zero due to the 90-degree phase shift. In some embodiments,a beginning of the high-current pulse could be determined by sensingwhen the source voltage V_(S) at the source capacitor C_(S) is at zero,at which point the high-current pulse through the laser diode D_(L)should begin.

For some applications, the amplitude of a high-current pulse deliveredby a resonant circuit such as any of those disclosed herein may need tobe adjusted in amplitude from pulse-to-pulse. Thus, in some embodiments,any of the pulsed laser drivers disclosed herein are advantageouslyoperable to configure an amplitude of the high-current pulse deliveredto one or more laser diodes on a pulse-to-pulse basis.

As shown in FIG. 17, FIG. 18, FIG. 19, and FIG. 20, the DC input voltageV_(in) is advantageously provided by an adjustable voltage supply (i.e.,a digital-to-analog converter (DAC)). In some embodiments, an outputvoltage level of the adjustable voltage supply is set using thecontroller 120. For example, FIG. 17 illustrates a pulsed laser diodedriver circuit 1701 that is the same as the pulsed laser diode driver101 shown in FIG. 1A with the exception that the DC input voltage V_(in)is generated by a DAC 1730. FIG. 18 illustrates a pulsed laser diodedriver circuit 1801 that is the same as the pulsed laser diode driver1301 shown in FIG. 13A with the exception that the DC input voltageV_(in) is generated by a DAC 1830. FIG. 19 illustrates a pulsed laserdiode driver circuit 1901 that is the same as the pulsed laser diodedriver 1308 shown in FIG. 13H with the exception that the DC inputvoltage V_(in) is generated by a DAC 1930. FIG. 20 illustrates a pulsedlaser diode driver circuit 2001 that is the same as the pulsed laserdiode driver 1501 shown in FIG. 15 with the exception that the DC inputvoltage V_(in) is generated by a DAC 2030. The examples shown in FIG.17, FIG. 18, FIG. 19, and FIG. 20 are merely select examples of pulsedlaser diode driver circuits configured to receive a DC input voltagefrom an adjustable voltage source (e.g., a DAC or a different adjustablevoltage source as is known in the art). In some embodiments, any of thepulsed laser diode drivers 101-103, 401-404, 501-504, 601-604, 701-705,801-802, 901-902, 1002-1004, 1301-1309, and/or 1501 are configured toreceive the DC input voltage V_(in) from an adjustable voltage sourcesuch as a DAC.

Use of an adjustable voltage supply, such as a DAC, to provide the DCinput voltage V_(in) to the pulsed laser diode driver circuits disclosedherein is possible because of the advantageously low input voltagerequirements for such embodiments. In some embodiments, the adjustablevoltage supply is clocked such that the adjustable voltage supplycharges the source capacitor C_(S) described herein only during a firstportion of a clock period (e.g., a positive portion). As such, the valueof the DC input voltage V_(in) and a current amplitude of thehigh-current pulse delivered to the laser diode(s) disclosed herein maybe advantageously varied between consecutive high-current pulses throughthe laser diode(s).

FIGS. 21A-21B show simplified plots, 2102 a-b, 2104 a-b, 2106 a-b, ofsignals related to operation of the pulsed laser diode drivers shown inFIGS. 17, 18, 19, and 20, in accordance with some embodiments.

FIG. 21A includes examples of high-current pulses 2102 a (i.e., throughthe laser diode(s) D_(L)), a source voltage V_(S) at the sourcecapacitor C_(S) 2106 a, and a linearly varying supply voltage 2106 a ofa variable input voltage supply (e.g., a DAC) that provides the DC inputvoltage V_(in). As shown, a current amplitude of the high-current pulses2102 a is advantageously varied from pulse to pulse.

FIG. 21B includes examples of high-current pulses 2102 b (i.e., throughthe laser diode(s) D_(L)), a source voltage V_(S) at the sourcecapacitor C_(S) 2106 b, and a stepped supply voltage of a variable inputvoltage supply (e.g., a DAC) that provides the DC input voltage V_(in).As shown, a current amplitude of the high-current pulses 2102 b isadvantageously varied from pulse to pulse. Although an output voltagetransition of the variable input voltage supply is fast, change in thesource voltage level V_(S) at the source capacitor C_(S) 2106 b islimited by the time constant of the source capacitor C_(S) and anon-resistance of an input switch (e.g., the source switch M_(S)described above) or an input resistor (e.g., the source resistor R_(S)described above).

Reference has been made in detail to embodiments of the disclosedinvention, one or more examples of which have been illustrated in theaccompanying figures. Each example has been provided by way ofexplanation of the present technology, not as a limitation of thepresent technology. In fact, while the specification has been describedin detail with respect to specific embodiments of the invention, it willbe appreciated that those skilled in the art, upon attaining anunderstanding of the foregoing, may readily conceive of alterations to,variations of, and equivalents to these embodiments. For instance,features illustrated or described as part of one embodiment may be usedwith another embodiment to yield a still further embodiment. Thus, it isintended that the present subject matter covers all such modificationsand variations within the scope of the appended claims and theirequivalents. These and other modifications and variations to the presentinvention may be practiced by those of ordinary skill in the art,without departing from the scope of the present invention, which is moreparticularly set forth in the appended claims. Furthermore, those ofordinary skill in the art will appreciate that the foregoing descriptionis by way of example only, and is not intended to limit the invention.

What is claimed is:
 1. A pulsed laser diode driver comprising: a firstinductor having a first terminal and a second terminal, the firstterminal of the first inductor being configured to receive a firstsource voltage, the first source voltage being based on a DC inputvoltage; a first source capacitor having a first terminal directlyelectrically connected to the first terminal of the first inductor toprovide the first source voltage and a second terminal electricallycoupled to ground; a first bypass switch having a drain node that isdirectly electrically connected to the second terminal of the firstinductor and a source node that is directly electrically connected toground; a first bypass capacitor having a first terminal directlyelectrically connected to the drain node of the first bypass switch; afirst laser diode having an anode and a cathode, the anode of the firstlaser diode being directly electrically connected to the second terminalof the first inductor and to the drain node of the first bypass switch;and a first laser diode switch having a drain node that is directlyelectrically connected to the cathode of the first laser diode and asource node that is directly electrically connected to ground; wherein:the first laser diode switch and the first bypass switch are configuredto control a current flow through the first inductor to produce ahigh-current pulse through the first laser diode, the high-current pulsecorresponding to a peak current of a resonant waveform developed at theanode of the first laser diode.
 2. The pulsed laser diode driver ofclaim 1, wherein: a second terminal of the first bypass capacitor isdirectly electrically connected to ground.
 3. The pulsed laser diodedriver of claim 1, wherein: a second terminal of the first bypasscapacitor is directly electrically connected to the second terminal ofthe first source capacitor.
 4. The pulsed laser diode driver of claim 1,wherein: a second terminal of the first bypass capacitor is directlyelectrically connected to the cathode of the first laser diode.
 5. Thepulsed laser diode driver of claim 1, further comprising: a resistorconfigured to receive the DC input voltage, the first source voltagebeing received at the first terminal of the first source capacitor viathe resistor.
 6. The pulsed laser diode driver of claim 1, furthercomprising: a source switch configured to receive the DC input voltage,the first source voltage being received at the first terminal of thefirst source capacitor via the source switch.
 7. The pulsed laser diodedriver of claim 1, further comprising: an adjustable voltage supplyconfigured to generate the DC input voltage.
 8. The pulsed laser diodedriver of claim 7, wherein: the adjustable voltage supply comprises aDigital-to-Analog Converter (DAC).
 9. The pulsed laser diode driver ofclaim 7, wherein: the adjustable voltage supply is configured to adjustthe DC input voltage between consecutive high-current pulses through thefirst laser diode.
 10. The pulsed laser diode driver of claim 1, furthercomprising: a second laser diode, an anode of the second laser diodebeing directly electrically connected to the anode of the first laserdiode.
 11. The pulsed laser diode driver of claim 1, further comprising:a second inductor having a first terminal and a second terminal, thefirst terminal of the second inductor being configured to receive asecond source voltage, the second source voltage being based on the DCinput voltage; a second source capacitor having a first terminaldirectly electrically connected to the first terminal of the secondinductor to provide the second source voltage and a second terminalelectrically coupled to ground; a second bypass switch having a drainnode that is directly electrically connected to the second terminal ofthe second inductor and a source node that is directly electricallyconnected to ground; a second bypass capacitor having a first terminaldirectly electrically connected to the drain node of the second bypassswitch; and a second laser diode having an anode and a cathode, theanode of the second laser diode being directly electrically connected tothe second terminal of the second inductor and to the drain node of thesecond bypass switch, the cathode of the second laser diode beingdirectly electrically connected to the drain node of the first laserdiode switch; wherein: the first laser diode switch and the secondbypass switch are configured to control a current flow through thesecond inductor to produce a high-current pulse through the second laserdiode, the high-current pulse corresponding to a peak current of aresonant waveform developed at the anode of the second laser diode. 12.The pulsed laser diode driver of claim 1, wherein: the second terminalof the first source capacitor is electrically coupled to ground via adamping resistor.
 13. The pulsed laser diode driver of claim 1, wherein:the second terminal of the first source capacitor is electricallycoupled to ground via a direct electrical connection to ground.
 14. Thepulsed laser diode driver of claim 1, wherein: the first laser diodeswitch is a Silicon-based field-effect transistor.
 15. A pulsed laserdiode driver comprising: an inductor having a first terminal and asecond terminal, the first terminal of the inductor being configured toreceive a source voltage; a source capacitor having a first capacitorterminal directly electrically connected to the first terminal of theinductor to provide the source voltage and a second capacitor terminalelectrically coupled to a bias voltage node; a source switch having afirst terminal that is directly electrically connected to a DC inputvoltage terminal and a second terminal that is directly electricallyconnected to the first capacitor terminal, the source switch beingoperable to charge the source capacitor when the source switch isenabled; a bypass switch having a drain node that is directlyelectrically connected to the second terminal of the inductor and asource node that is directly electrically connected to the bias voltagenode; a laser diode switch having a drain node that is directlyelectrically connected to the second terminal of the inductor and to thedrain node of the bypass switch; a laser diode having an anode that isdirectly electrically connected to a source node of the laser diodeswitch and a cathode that is directly electrically connected to the biasvoltage node; and a bypass capacitor having i) a first terminal directlyelectrically connected to the second terminal of the inductor and asecond terminal directly electrically connected to the bias voltagenode, ii) a first terminal directly electrically connected to the anodeof the laser diode and a second terminal directly electrically connectedto the bias voltage node, iii) a first terminal directly electricallyconnected to the second terminal of the inductor and a second terminaldirectly electrically connected to the second capacitor terminal of thesource capacitor, or iv) a first terminal directly electricallyconnected to the anode of the laser diode and a second terminal directlyelectrically connected to the second capacitor terminal of the sourcecapacitor; wherein: the laser diode switch and the bypass switch areconfigured to control a current flow through the inductor to produce ahigh-current pulse through the laser diode, the high-current pulsecorresponding to a peak current of a resonant waveform developed at theanode of the laser diode.
 16. The pulsed laser diode driver of claim 15,further comprising: an adjustable voltage supply configured to provide aDC input voltage to the DC input voltage terminal.
 17. A pulsed laserdiode driver comprising: an inductor having a first terminal and asecond terminal, the first terminal being configured to receive a sourcevoltage; a source capacitor having a first capacitor terminal directlyelectrically connected to the first terminal of the inductor to providethe source voltage and a second capacitor terminal electrically coupledto a bias voltage node; a source switch having a first terminal that isdirectly electrically connected to a DC input voltage terminal and asecond terminal that is directly electrically connected to the firstcapacitor terminal, the source switch being operable to charge thesource capacitor when the source switch is enabled; a bypass switchhaving a drain node that is directly electrically connected to thesecond terminal of the inductor and a source node that is directlyelectrically connected to the bias voltage node; a laser diode having ananode and a cathode, the anode being directly electrically connected tothe second terminal of the inductor and to the drain node of the bypassswitch; a laser diode switch having a drain node that is directlyelectrically connected to the cathode of the laser diode and a sourcenode that is directly electrically connected to the bias voltage node;and a bypass capacitor having i) a first terminal directly electricallyconnected to the second terminal of the inductor and a second terminaldirectly electrically connected to the bias voltage node, ii) a firstterminal directly electrically connected to the second terminal of theinductor and a second terminal directly electrically connected to thesecond capacitor terminal of the source capacitor, or iii) a firstterminal directly electrically connected to the anode of the laser diodeand a second terminal directly electrically connected to the cathode ofthe laser diode; wherein, the laser diode switch and the bypass switchare configured to control a current flow through the inductor to producea high-current pulse through the laser diode, the high-current pulsecorresponding to a peak current of a resonant waveform developed at theanode of the laser diode.
 18. The pulsed laser diode driver of claim 17,further comprising: an adjustable voltage supply configured to provide aDC input voltage to the DC input voltage terminal.
 19. A pulsed laserdiode driver comprising: a plurality of inductors, each inductor havinga first terminal and a second terminal, the first terminal of eachinductor being configured to receive a respective source voltage; aplurality of source capacitors, each source capacitor corresponding to arespective inductor and having a first capacitor terminal directlyelectrically connected to the first terminal of that respective inductorto provide the respective source voltage and a second capacitor terminalelectrically coupled to a bias voltage node; a plurality of bypassswitches, each bypass switch corresponding to a respective inductor andhaving a drain node that is directly electrically connected to thesecond terminal of that respective inductor and a source node that isdirectly electrically connected to the bias voltage node; a plurality oflaser diodes, each laser diode corresponding to a respective inductorand a respective bypass switch and having an anode and a cathode, theanode being directly electrically connected to the second terminal ofthat respective inductor and to the drain node of that respective bypassswitch; a laser diode switch having a drain node that is directlyelectrically connected to the cathode of each of the laser diodes and asource node that is directly electrically connected to the bias voltagenode; and a plurality of bypass capacitors, each bypass capacitorcorresponding to a respective inductor and having a first terminaldirectly electrically connected to the second terminal of thatrespective inductor and a second terminal directly electricallyconnected to the bias voltage node; wherein, the laser diode switch andthe plurality of bypass switches are configured to control a respectivecurrent flow through each of the inductors to produce a respectivehigh-current pulse through each of the laser diodes, each of thehigh-current pulses corresponding to a peak current of a resonantwaveform developed at the anode of a respective laser diode.
 20. Thepulsed laser diode driver of claim 19, further comprising: a pluralityof source switches configured to receive a DC input voltage and toprovide the respective source voltages to the plurality of sourcecapacitors.